General - Accounts Receivable, Contract Assets and Contract Liabilities - Tabular Disclosure (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Summary of Significant Accounting Policies
Accounts receivable	$ 824,067	$ 799,803
Change in accounts receivable	$ 24,264
Change in accounts receivable (as a percent)	3.00%
Contract assets	$ 4,678	3,566
Change in contract assets	$ (1,112)
Change in contract assets (as a percent)	31.20%
Contract liabilities - current	$ 6,968	6,772
Change in contract liabilities - current	$ 196
Change in contract liabilities - current (as a percent)	2.90%
Contract liabilities - long-term	$ 11,453	$ 11,073
Change in contract liabilities - long-term	$ 380
Change in contract liabilities - long-term (as a percent)	3.40%