Goodwill and Other Intangible Assets (Schedule of Other Intangible Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 485,202	$ 485,237
Accumulated Amortization	302,968	283,006
Net Carrying Amount	182,234	202,231
Contract and program intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	430,632	430,632
Accumulated Amortization	256,859	242,194
Net Carrying Amount	173,773	188,438
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	54,570	54,605
Accumulated Amortization	46,109	40,812
Net Carrying Amount	$ 8,461	$ 13,793