Fair Value of Financial Instruments and Concentrations of Credit Risk (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of Accounts Receivable
Gross trade receivables	$ 306,791	$ 193,349
Allowance for doubtful accounts	(3,161)	(5,839)	(5,969)	(4,259)
Net trade receivables	303,630	187,510
Other receivables	24,960	9,289
Total receivables, net	$ 328,590	$ 196,799