Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 518,402	$ 481,423
Allowance for doubtful accounts and other reserves	(1,745)	(1,534)
Accounts receivable, net	516,657	479,889
Unbilled accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	161,352	143,978
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 357,050	$ 337,445