Description of Business and Summary of Significant Accounting Policies - Accounts Receivables and Allowances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 146,623		$ 146,623		$ 142,847
Allowance for doubtful accounts	19,489		19,489		22,691
Provision for doubtful accounts	73	$ 474	(2,742)	$ 424
Billed Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	146,600		146,600		142,800
Unbilled Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 46,600		$ 46,600		$ 45,200