Acquisitions - Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed on Preliminary Purchase Price Allocation (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Nov. 19, 2020
Business Acquisition [Line Items]
Contract assets	$ 568,239	$ 576,568
Goodwill	1,263,060	1,261,978
Contract liabilities	$ (196,547)	$ (201,864)
Braxton Science & Technology Group
Business Acquisition [Line Items]
Cash and cash equivalents			$ 7,006
Accounts receivable			18,163
Contract assets			8,350
Prepaid expenses and other current assets			3,036
Property and equipment			5,114
Right of use assets, operating leases			10,788
Goodwill			212,185
Intangible assets			74,950
Accounts payable			(7,464)
Accrued expenses and other current liabilities			(9,845)
Contract liabilities			(300)
Short-term lease liabilities, operating leases			(1,915)
Long-term lease liabilities, operating leases			(8,873)
Deferred tax liabilities			(1,694)
Net assets acquired			$ 309,501