Accounts Receivable - Schedule of Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 308,887	$ 275,691
Allowance for doubtful accounts	(754)	(708)
Reserve for cash-basis customers	(6,179)	(2,995)
Total accounts receivable reserves	(6,933)	(3,703)
Accounts receivable, net	301,954	271,988
Trade accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	218,310	175,391
Unbilled accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross accounts receivable	$ 90,577	$ 100,300