Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 387,763	$ 338,601
Allowance for doubtful accounts	(906)	(1,033)
Reserve for cash-basis customers	(6,458)	(7,990)
Total accounts receivable reserves	(7,364)	(9,023)
Accounts receivable, net	380,399	329,578
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	262,885	222,531
Unbilled Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 124,878	$ 116,070