Accounts Receivable - Schedule of Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 374,964	$ 338,601
Allowance for doubtful accounts	(641)	(1,033)
Reserve for cash-basis customers	(8,366)	(7,990)
Total accounts receivable reserves	(9,007)	(9,023)
Accounts receivable, net	365,957	329,578
Unbilled accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	123,053	116,070
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 251,911	$ 222,531