Accounts Receivable Schedule of Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 260,037	$ 222,584
Allowance for doubtful accounts	(824)	(1,154)
Reserve for cash-basis customers	(2,760)	(2,653)
Accounts receivable reserve	(3,584)	(3,807)
Accounts receivable, net	256,453	218,777
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	169,873	143,533
Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 90,164	$ 79,051