Summary of Significant Accounting Policies - Accounts Receivable, Contract Assets and Contract Liabilities - Tabular Disclosure (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies
Accounts receivable	$ 799,803	$ 717,455
Change in accounts receivable	$ 82,348
Change in accounts receivable (as a percent)	11.50%
Contract assets	$ 3,566	2,162
Change in contract assets	$ 1,404
Change in contract assets (as a percent)	64.90%
Contract liabilities - current	$ 6,772	6,728
Change in contract liabilities - current	$ 44
Change in contract liabilities - current (as a percent)	0.70%
Contract liabilities - long-term	$ 11,073	$ 11,099
Change in contract liabilities - long-term	$ (26)
Change in contract liabilities - long-term (as a percent)	(0.20%)