Description of Business and Summary of Significant Accounting Policies - Accounts Receivables and Allowances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 146,568		$ 142,847
Allowance for doubtful accounts	20,544		22,691
Provision for doubtful accounts	(2,060)	$ (618)
Billed Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	146,600		142,800
Unbilled Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 51,300		$ 45,200