Statement of Financial Position [Abstract] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, authorized (in shares) Common Stock, Shares Authorized Common stock, issued (in shares) Common Stock, Shares, Issued Common stock, outstanding (in shares) Common Stock, Shares, Outstanding Treasury stock (in shares) Treasury Stock, Shares Revenue from Contract with Customer [Abstract] Revenue Revenue from Contract with Customer [Text Block] Leases [Abstract] Remainder of 2020 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2021 Lessee, Operating Lease, Liability, Payments, Due Year Two 2022 Lessee, Operating Lease, Liability, Payments, Due Year Three 2023 Lessee, Operating Lease, Liability, Payments, Due Year Four 2024 Lessee, Operating Lease, Liability, Payments, Due Year Five Thereafter Lessee, Operating Lease, Liability, Payments, Due after Year Five Total future lease payments Lessee, Operating Lease, Liability, Payments, Due Less: imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Total lease liabilities Operating Lease, Liability Organization, Consolidation and Presentation of Financial Statements [Abstract] Accounting Estimates Use of Estimates, Policy [Policy Text Block] Recently Adopted Accounting Standards and Recent Accounting Pronouncements Not Yet Adopted New Accounting Pronouncements, Policy [Policy Text Block] Number of reportable segments Number of Operating Segments Number of employees Entity Number of Employees Commitments and Contingencies Disclosure [Abstract] Concentration Risk [Table] Concentration Risk [Table] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Financial Standby Letter of Credit Financial Standby Letter of Credit [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Contracts with U.S. government agencies or other U.S. government contractors Government Contracts Concentration Risk [Member] Concentration Risk [Line Items] Concentration Risk [Line Items] Guarantor obligations, carrying value Guarantor Obligations, Current Carrying Value Guarantor obligations, reduction to available borrowings Guarantor Obligations, Liquidation Proceeds, Monetary Amount Guarantor obligations, facility Guarantor Obligations, Facility Guarantor Obligations, Facility Guarantor obligations, available amount Guarantor Obligations, Available Amount Guarantor Obligations, Available Amount Concentration risk, percentage Concentration Risk, Percentage Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Unfavorable Regulatory Action Unfavorable Regulatory Action [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Liability for reductions and/or penalties from U.S Government audits Loss Contingency Accrual Earnings Per Share [Abstract] Earnings Per Share Earnings Per Share [Text Block] Fair Value Disclosures [Abstract] Schedule of Recurring Fair Value Measurements Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Cost of revenue Cost of Sales [Member] General and administrative expenses General and Administrative Expense [Member] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Stock options Share-based Payment Arrangement, Option [Member] Restricted stock Restricted Stock [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] EIP Amended and Restated Equity Incentive Plan [Member] Amended and Restated Equity Incentive Plan [Member] Annual Incentive Plan Annual Incentive Plan [Member] Annual Incentive Plan [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Class A Common Stock Common Class A [Member] Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Stock-based compensation expense Share-based Payment Arrangement, Expense Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Affiliated Entity Affiliated Entity [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Services Performed Under Subcontractor Services Performed Under Subcontractor [Member] Services Performed Under Subcontractor [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Number of directors Number of Directors Number of Directors Payments to related party Related Party Transaction, Amounts of Transaction Retirement Benefits [Abstract] Employer matching contribution, percent of match Defined Contribution Plan, Employer Matching Contribution, Percent of Match Employees’ capital accumulation plan, total expense recognized Defined Contribution Plan, Cost Employees’ capital accumulation plan, company-paid contributions Defined Contribution Plan, Employer Discretionary Contribution Amount Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Retirement Plan Name [Axis] Retirement Plan Name [Axis] Retirement Plan Name [Domain] Retirement Plan Name [Domain] Officer Medical Plan Officer Medical Plan [Member] Officer Medical Plan [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Supplemental Employee Retirement Plan Supplemental Employee Retirement Plan [Member] Other Postretirement Benefits Plan Other Postretirement Benefits Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Deferred compensation arrangement with individual, annual cash award granted per year of service, amount Deferred Compensation Arrangement with Individual, Annual Cash Award Granted per Year of Service, Amount Deferred Compensation Arrangement with Individual, Annual Cash Award Granted per Year of Service, Amount Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Net actuarial loss Defined Benefit Plan, Amortization of Gain (Loss) Total postretirement medical expense Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Defined benefit plan, unfunded status of plan Defined Benefit Plan, Funded (Unfunded) Status of Plan Long-term disability obligation Postemployment Benefits Liability, Noncurrent Maximum eligible deferral of compensation, percentage Deferred Compensation Plans, Maximum Eligible Deferral of Compensation, Percentage Deferred Compensation Plans, Maximum Eligible Deferral of Compensation, Percentage Deferred compensation plan, assets Deferred Compensation Plan Assets Deferred compensation plan, liabilities Deferred Compensation Liability, Classified, Noncurrent Other Liabilities Disclosure [Abstract] Deferred rent Deferred Rent Credit, Noncurrent Postretirement benefit obligations Liability, Pension and Other Postretirement and Postemployment Benefits, Noncurrent Other Other Liabilities and Deferred Revenue, Noncurrent Total other long-term liabilities Other Liabilities, Noncurrent Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Secured Debt Secured Debt [Member] Revolving Credit Facility Revolving Credit Facility [Member] Letter of Credit Letter of Credit [Member] Senior Notes Senior Notes [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Delayed Draw Facility Delayed Draw Facility [Member] Delayed Draw Facility [Member] Term Loan A Tranche-A Loans [Member] Tranche A Loans [Member] Term Loan B Tranche B Loans [Member] Tranche B Loans [Member] Senior Notes due 2025 Senior Notes Due 2025 [Member] Senior Notes Due 2025 [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Overnight Federal Funds Rate Overnight Federal Funds Rate [Member] Overnight Federal Funds Rate Base Rate Base Rate [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Revolving credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Long-term debt, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Long-term debt outstanding Long-term Debt, Gross Proceeds from lines of credit Proceeds from Lines of Credit Long-term debt, maximum expanded loan facility Long-term Debt, Maximum Expanded Loan Facility Long-Term Debt, Maximum Expanded Loan Facility Percentage of consolidated EBITDA required for expansion of loan Debt Covenant, Expanded Loan, Percentage of Consolidated EBITDA Required Debt Covenant, Expanded Loan, Percentage of Consolidated EBITDA Required Net secured leverage ratio Debt Instrument, Net Secured Leverage Ratio, Maximum Debt Instrument, Net Secured Leverage Ratio, Maximum Commitment fee percentage Line of Credit Facility, Commitment Fee Percentage Revolving credit facility, amount outstanding Long-term Line of Credit Quarterly periodic payment percentage, principal Debt Instrument, Quarterly Periodic Payment Percentage, Principal Debt Instrument, Quarterly Periodic Payment Percentage, Principal Interest payments Interest Paid, Including Capitalized Interest, Operating and Investing Activities Term loan, face amount Debt Instrument, Face Amount Debt instrument, stated percentage Debt Instrument, Interest Rate, Stated Percentage Debt issuance costs Debt Issuance Costs, Gross Notional amount of interest rate swaps Derivative, Notional Amount Stock-Based Compensation Share-based Payment Arrangement [Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative [Table] Derivative [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging Cash Flow Hedging [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Current Assets Other Current Assets [Member] Long-term assets Other Noncurrent Assets [Member] Other Current Liabilities Other Current Liabilities [Member] Other Noncurrent Liabilities Other Noncurrent Liabilities [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Forward Starting Floating-To-Fixed Interest Rate Swap Forward Starting Floating-To-Fixed Interest Rate Swap [Member] Forward Starting Floating-To-Fixed Interest Rate Swap [Member] Interest Rate Swap Interest Rate Swap [Member] Derivative [Line Items] Derivative [Line Items] Number of interest rate swap agreements entered into during period Derivatives, Number Of Agreements Entered Into During The Period Derivatives, Number Of Agreements Entered Into During The Period Number of financial institutions Derivatives, Number Of Financial Institutions Derivatives, Number Of Financial Institutions Derivative, Notional Amount Fair value of derivative liabilities Derivative Instruments in Hedges, Liabilities, at Fair Value Fair value of derivative assets Derivative Instruments in Hedges, Assets, at Fair Value Estimate of amount to be reclassified over the next 12 months Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Operating lease right-of-use assets Operating Lease, Right-of-Use Asset Deferred tax liability corresponding to operating lease right-of-use assets Operating Lease, Right-of-Use Asset, Deferred Tax Liability Operating Lease, Right-of-Use Asset, Deferred Tax Liability Deferred tax asset corresponding to operating lease liabilities Operating Lease, Liability, Deferred Tax Asset Operating Lease, Liability, Deferred Tax Asset Operating lease, deferred rent and tenant allowances Operating Lease, Liability, Deferred Rent and Tenant Allowances Operating Lease, Liability, Deferred Rent and Tenant Allowances Equity [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Post-retirement plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Derivatives designated as cash flow hedges Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Derivatives designated as cash flow hedges Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Totals AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning of period Stockholders' Equity Attributable to Parent Other comprehensive income (loss) before reclassifications OCI, before Reclassifications, Net of Tax, Attributable to Parent Amounts reclassified from accumulated other comprehensive loss Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Total other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent End of period Other comprehensive income (loss) before reclassifications, tax Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Schedules of Lease Cost Lease, Cost [Table Text Block] Schedule of Future Minimum Operating Lease Payments Lessee, Operating Lease, Liability, Maturity [Table Text Block] Statement of Cash Flows [Abstract] Cash flows from operating activities Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss) Attributable to Parent Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Noncash lease expense Noncash Lease Expense Noncash Lease Expense Stock-based compensation expense Share-based Payment Arrangement, Noncash Expense Amortization of debt issuance costs and loss on extinguishment Amortization of Debt Issuance Costs and Loss On Debt Extinguishment Amortization of Debt Issuance Costs and Loss On Debt Extinguishment Losses on dispositions Gain (Loss) on Disposition of Assets Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable, net of allowance Increase (Decrease) in Accounts Receivable Deferred income taxes and income taxes receivable / payable Increase (Decrease) in Income Taxes Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Other long-term assets Increase (Decrease) in Other Noncurrent Assets Accrued compensation and benefits Increase (Decrease) in Employee Related Liabilities Accounts payable and other accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Other current liabilities Increase (Decrease) in Other Operating Liabilities Operating lease liabilities Increase (Decrease) In Operating Lease Liabilities Increase (Decrease) In Operating Lease Liabilities Other long-term liabilities Increase (Decrease) in Other Noncurrent Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of property, equipment, and software Payments to Acquire Productive Assets Payments for business acquisitions, net of cash acquired Payments for (Proceeds from) Businesses and Interest in Affiliates Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from issuance of common stock Proceeds from Issuance of Common Stock Stock option exercises Proceeds from Stock Options Exercised Repurchases of common stock Payments for Repurchase of Common Stock Cash dividends paid Payments of Dividends Repayment of debt Repayments of Debt Proceeds from debt issuance Proceeds from Issuance of Long-term Debt Other financing activities Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Cash and cash equivalents––beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents––end of period Supplemental disclosures of cash flow information Supplemental Cash Flow Information [Abstract] Net cash paid during the period for: Cash Payments Abstract Cash paid during the period for: Interest Interest Paid, Excluding Capitalized Interest, Operating Activities Income taxes Income Taxes Paid, Net Supplemental disclosures of non-cash investing and financing activities Noncash Investing and Financing Items [Abstract] Noncash financing activities Noncash Financing Activities Noncash Financing Activities Schedule of Derivative Instruments Schedule of Derivative Instruments [Table Text Block] Revenue, amount of remaining performance obligation Revenue, Remaining Performance Obligation, Amount Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Remaining performance obligation, expected timing, period one Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period One Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period One Remaining performance obligation, expected timing, period two Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Two Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Two Remaining performance obligation, percentage Revenue, Remaining Performance Obligation, Percentage Contract with customer, liability, revenue recognized Contract with Customer, Liability, Revenue Recognized Other Long-Term Liabilities Other Liabilities Disclosure [Text Block] Cash paid for amounts included in the measurement of lease liabilities Operating Lease, Payments Operating lease liabilities arising from obtaining ROU assets (1) Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Weighted average remaining lease term (in years) Operating Lease, Weighted Average Remaining Lease Term Weighted average discount rate (as a percent) Operating Lease, Weighted Average Discount Rate, Percent Operating lease cost Operating Lease, Cost Short-term lease cost Short-term Lease, Cost Variable lease cost Variable Lease, Cost Total operating lease costs Lease, Cost Components of net postretirement medical expense Schedule of Net Benefit Costs [Table Text Block] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-02 Accounting Standards Update 2016-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Current assets: Assets, Current [Abstract] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Non-current assets: Assets, Noncurrent [Abstract] Operating lease right-of-use assets Other long-term assets Other Assets, Noncurrent Current liabilities: Liabilities, Current [Abstract] Accounts payable and other accrued expenses Accounts Payable and Accrued Liabilities, Current Operating lease liabilities Operating Lease, Liability, Current Non-current liabilities: Liabilities, Noncurrent [Abstract] Operating lease liabilities, net of current portion Operating Lease, Liability, Noncurrent Other long-term liabilities Income Statement [Abstract] Revenue Revenue from Contract with Customer, Excluding Assessed Tax Operating costs and expenses: Costs and Expenses [Abstract] Cost of revenue Cost of Goods and Services Sold Billable expenses Billable Expenses Billable expenses include direct subcontractor expenses, travel expenses, and other expenses incurred to perform on contracts. General and administrative expenses General and Administrative Expense Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Total operating costs and expenses Costs and Expenses Operating income Operating Income (Loss) Interest expense Interest Expense Other income (expense), net Other Nonoperating Income (Expense) Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Earnings per common share (Note 4): Basic (in dollars per share) Earnings Per Share, Basic Diluted (in dollars per share) Earnings Per Share, Diluted Schedule of Debt Schedule of Debt [Table Text Block] Schedule of Interest Expense Interest Income and Interest Expense Disclosure [Table Text Block] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Amount of Gain or (Loss) Recognized in AOCI on Derivatives Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification and Tax Amount of Gain or (Loss) Reclassified from AOCI into Income Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Interest Expense on Condensed Consolidated Statements of Operations Receivables [Abstract] Schedule of Accounts Receivable, Net of Allowance Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Accounts Receivable, Net of Allowance Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Other noncurrent liabilities Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Recurring [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets, Fair Value Disclosure [Abstract] Assets, Fair Value Disclosure [Abstract] Current derivative instruments Derivative Asset, Current Long term derivative instruments Derivative Asset, Noncurrent Long term deferred compensation costs Total Assets Other Assets, Fair Value Disclosure Liabilities, Fair Value Disclosure [Abstract] Liabilities, Fair Value Disclosure [Abstract] Contingent consideration, liability Business Combination, Contingent Consideration, Liability, Noncurrent Current derivative instruments Derivative Liability, Current Long term derivative instruments Derivative Liability, Noncurrent Long term deferred compensation costs Total Liabilities Financial Liabilities Fair Value Disclosure Payables and Accruals [Abstract] Schedule of Accounts Payable and Accrued Liabilities Schedule of Accounts Payable and Accrued Liabilities [Table Text Block] Accounts Payable and Other Accrued Expenses Accounts Payable and Accrued Liabilities Disclosure [Text Block] Current assets Contract with Customer, Asset, Net, Current [Abstract] Accounts receivable–billed Billed Contracts Receivable Accounts receivable–unbilled Contract with Customer, Asset, Net, Current Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Current Accounts receivable, net of allowance Accounts Receivable, after Allowance for Credit Loss, Current Other long-term assets Contract with Customer, Asset, Net, Noncurrent [Abstract] Accounts receivable–unbilled Contract with Customer, Asset, Net, Noncurrent Total accounts receivable, net Accounts Receivable, after Allowance for Credit Loss Provision for doubtful accounts Accounts Receivable, Credit Loss Expense (Reversal) Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Tax Period [Axis] Tax Period [Axis] Tax Period [Domain] Tax Period [Domain] Tax Years 2013-2015 Tax Years 2013-2015 [Member] Tax Years 2013-2015 [Member] Tax Years 2016-2019 Tax Years 2016-2019 [Member] Tax Years 2016-2019 [Member] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Federal statutory rate (as a percent) Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Income tax assessments Income Tax Examination, Estimate of Possible Loss Income tax uncertainty Liability for Uncertainty in Income Taxes, Noncurrent Schedule of Earnings Per Share, Basic, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Basic, by Common Class, Including Two Class Method [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings for basic computations Undistributed Earnings, Basic Weighted-average common shares outstanding for basic computations (in shares) Weighted Average Number of Shares Outstanding, Basic Earnings for diluted computations Undistributed Earnings, Diluted Dilutive stock options and restricted stock (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Weighted-average common shares outstanding for diluted computations (in shares) Weighted Average Number of Shares Outstanding, Diluted Earnings per common share Earnings Per Share Reconciliation [Abstract] Unvested shares participating in the payment of the Company's dividends declared (in shares) Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Unvested shares, cash dividends paid Undistributed earnings allocated to participating securities, basic Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Undistributed earnings allocated to participating securities, diluted Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted Antidilutive options excluded from the computation of EPS (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Compensation Related Costs [Abstract] Accrued Compensation and Benefits Compensation Related Costs, General [Text Block] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Business Overview Nature of Operations [Text Block] Contract assets: Contract with Customer, Asset, after Allowance for Credit Loss [Abstract] Current Long-term Total Contract with Customer, Asset, after Allowance for Credit Loss Contract liabilities: Contract with Customer, Liability [Abstract] Advance payments, billings in excess of costs incurred and deferred revenue Contract with Customer, Liability Schedule of accumulated other comprehensive loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Reclassification out of accumulated other comprehensive loss to net income Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Employee Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Restricted stock units (RSUs) Restricted Stock Units (RSUs) [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Stock options outstanding (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Stock options outstanding, unvested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares Restricted stock granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Restricted stock, total fair value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Fair Value Stock price on grant date (in dollars per share) Share Price Stock purchased by employees (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Cover page. Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Current Fiscal Year End Date Current Fiscal Year End Date Entity Central Index Key Entity Central Index Key Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Debt Debt Disclosure [Text Block] Bonus Accrued Bonuses, Current Retirement Liability, Pension and Other Postretirement and Postemployment Benefits, Current Vacation Accrued Vacation, Current Other Other Employee-related Liabilities, Current Total accrued compensation and benefits Employee-related Liabilities, Current Summary of Stock-Based Compensation Expense Recognized in the Condensed Consolidated Statements of Operations Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Schedule of Unrecognized Compensation Cost Share-based Payment Arrangement, Nonvested Award, Cost [Table Text Block] Senior Notes Long-term Debt, Current and Noncurrent [Abstract] Long-term Debt, Current and Noncurrent [Abstract] Interest rate Debt Instrument, Interest Rate, Effective Percentage Less: Unamortized debt issuance costs and discount on debt Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Total Long-term Debt Less: Current portion of long-term debt Long-term Debt, Current Maturities Long-term debt, net of current portion Long-term Debt, Excluding Current Maturities Summary of Other Long-Term Liabilities Schedule of Other Assets and Other Liabilities [Table Text Block] Unrecognized compensation cost related to unvested stock-based compensation agreements Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Unrecognized compensation cost, amortization period Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Schedule of New Accounting Pronouncements and Changes in Accounting Principles Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Related-Party Transactions Related Party Transactions Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Treasury Stock Treasury Stock [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income (Loss) Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (shares) Shares, Outstanding Issuance of common stock (shares) Stock Issued During Period, Shares, New Issues Issuance of common stock Stock Issued During Period, Value, New Issues Stock options exercised (shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Stock options exercised Stock Issued During Period, Value, Stock Options Exercised Repurchase of common stock (shares) Treasury Stock, Shares, Acquired Repurchase of common stock Treasury Stock, Value, Acquired, Cost Method Recognition of liability related to future restricted stock units vesting APIC, Share-based Payment Arrangement, Option, Increase for Cost Recognition Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Dividends paid per common share Dividends, Cash Stock-based compensation expense APIC, Share-based Payment Arrangement, Increase for Cost Recognition Ending balance (shares) Derivatives Derivative Instruments and Hedging Activities Disclosure [Text Block] Vendor payables Accounts Payable, Trade, Current Accrued expenses Accrued Liabilities, Current Total accounts payable and other accrued expenses Reconciliation of the income used to compute basic and diluted EPS Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Dividends paid (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Repurchase of common stock (in shares) Repurchase of common stock, value Statement of Comprehensive Income [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Change in unrealized (loss) gain on derivatives designated as cash flow hedges Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Change in unrealized (loss) gain on derivatives designated as cash flow hedges Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Change in postretirement plan costs Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Cost-reimbursable Cost Reimbursable Contract [Member] Cost Reimbursable Contract Time-and-materials Time-and-materials Contract [Member] Fixed-price Fixed-price Contract [Member] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Defense Clients Defense Clients [Member] Defense Clients [Member] Intelligence Clients Intelligence Clients [Member] Intelligence Clients [Member] Civil Clients Civil Clients [Member] Civil Clients [Member] Global Commercial Clients Global Commercial Clients [Member] Global Commercial Clients [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] UNITED STATES UNITED STATES Contract with Customer, Sales Channel [Axis] Contract with Customer, Sales Channel [Axis] Customer [Domain] Contract with Customer, Sales Channel [Domain] Prime Contractor Sales Channel, Directly to Consumer [Member] Sub-contractor Sales Channel, Through Intermediary [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Total revenue (as a percent) Revenue From Contract With Customer, Excluding Assessed Tax, Percentage Revenue From Contract With Customer, Excluding Assessed Tax, Percentage Fair Value Measurements Fair Value Disclosures [Text Block] Accumulated Other Comprehensive Loss Comprehensive Income (Loss) Note [Text Block] Interest expense on debt Interest Expense, Debt Deferred Payment Obligation Interest Deferred Payment Obligation, Interest Payment Deferred Payment Obligation, Interest Payment Amortization of Debt Issuance Cost (DIC) and Original Issue Discount (OID) Amortization of Debt Issuance Costs and Discounts Other Interest Income (Expense), Other Interest Income (Expense), Other Total Interest Expense Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Summary of Contract Balances Contract with Customer, Asset and Liability [Table Text Block] Schedule of accrued compensation and benefits Schedule of Accrued Compensation And Benefits [Table Text Block] Schedule of Accrued Compensation And Benefits [Table Text Block] Leases Lessee, Operating Leases [Text Block] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] United States District Court for the Eastern District of Virginia styled Langley v. Booz Allen Hamilton Holding Corp. United States District Court For The Eastern District Of Virginia Styled Langley V. Booz Allen Hamilton Holding Corp. [Member] United States District Court for the Eastern District of Virginia styled Langley v. Booz Allen Hamilton Holding Corp. [Member] Former stockholder litigation Former Stockholder Litigation [Member] Former Stockholder Litigation [Member] Litigation Court [Axis] Litigation Court [Axis] Litigation Court [Axis] Litigation Court Type [Domain] Litigation Court Type [Domain] Litigation Court Type [Domain] United States District Court for Southern District of New York United States District Court for Southern District of New York [Member] United States District Court for Southern District of New York [Member] Loss contingencies, number of plaintiffs Loss Contingency, Number of Plaintiffs Loss contingencies, new claims filed, number Loss Contingency, New Claims Filed, Number Loss contingencies, claims amended, number Loss Contingency, Claims Amended, Number Loss Contingency, Claims Amended, Number Loss contingencies, claims dismissed, number Loss Contingency, Claims Settled and Dismissed, Number Loss contingency, claims amended, number of claims consolidated Loss Contingency, Claims Amended, Number Of Claims Consolidated Loss Contingency, Claims Amended, Number Of Claims Consolidated Loss contingencies, claims settled, number Loss Contingency, Claims Settled, Number Loss contingencies, pending claims, number Loss Contingency, Pending Claims, Number ASSETS Assets [Abstract] Current assets: Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable, net of allowance Total current assets Assets, Current Property and equipment, net of accumulated depreciation Property, Plant and Equipment, Net Intangible assets, net of accumulated amortization Intangible Assets, Net (Excluding Goodwill) Goodwill Goodwill Total assets Assets LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Current liabilities: Current portion of long-term debt Accounts payable and other accrued expenses Accrued compensation and benefits Other current liabilities Other Liabilities, Current Total current liabilities Liabilities, Current Total liabilities Liabilities Commitments and contingencies (Note 18) Commitments and Contingencies Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock, Class A — $0.01 par value — authorized, 600,000,000 shares; issued, 160,400,357 shares at September 30, 2019 and 159,924,825 shares at March 31, 2019; outstanding, 140,373,450 shares at September 30, 2019 and 140,027,853 shares at March 31, 2019 Common Stock, Value, Issued Treasury stock, at cost — 20,026,907 shares at September 30, 2019 and 19,896,972 shares at March 31, 2019 Treasury Stock, Value Additional paid-in capital Additional Paid in Capital, Common Stock Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total stockholders’ equity Total liabilities and stockholders’ equity Liabilities and Equity Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Post-retirement Plans Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Reclassification out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Income before income taxes Tax benefit (expense)