Accounts Receivable Schedule of Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 275,691	$ 222,584
Allowance for doubtful accounts	(708)	(1,154)
Reserve for cash-basis customers	(2,995)	(2,653)
Total accounts receivable reserves	(3,703)	(3,807)
Accounts receivable, net	271,988	218,777
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	175,391	143,533
Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 100,300	$ 79,051