Description of Business and Summary of Significant Accounting Policies - Accounts Receivables and Allowances (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 142,360		$ 142,360		$ 142,847
Allowance for doubtful accounts	19,439		19,439		22,691
Provision for doubtful accounts	(755)	$ 568	(2,815)	$ (50)
Billed Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	142,400		142,400		142,800
Unbilled Revenues
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 46,100		$ 46,100		$ 45,200