Details of Selected Balance Sheet Accounts - Accounts Receivable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	$ 231,158		$ 242,232
Allowance for doubtful accounts	(8,686)		(8,745)
Accounts receivable, net	$ 222,472		233,487
Allowance for doubtful accounts as a percentage of total accounts receivable	4.00%	4.00%
Trade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	$ 174,041		178,813
Unbilled revenue
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	29,086		28,341
Contract assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	23,148		26,034
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	$ 4,883		$ 9,044