Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 354,623	$ 338,601
Allowance for doubtful accounts	(977)	(1,033)
Reserve for cash-basis customers	(10,716)	(7,990)
Total accounts receivable reserves	(11,693)	(9,023)
Accounts receivable, net	342,930	329,578
Unbilled accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	118,509	116,070
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 236,114	$ 222,531