Accounts Receivable - Schedule of Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 366,595	$ 338,601
Allowance for doubtful accounts	(863)	(1,033)
Reserve for cash-basis customers	(9,103)	(7,990)
Total accounts receivable reserves	(9,966)	(9,023)
Accounts receivable, net	356,629	329,578
Unbilled accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	121,327	116,070
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 245,268	$ 222,531