Trade Accounts Receivable, Net (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Trade Accounts Receivable, Net
Trade accounts receivable	$ 123,531	$ 78,642	$ 121,414
Allowance for doubtful accounts	(1,343)	(991)	(1,500)
Allowance for sales discounts and returns	(2,069)	(1,231)	(1,939)
Trade accounts receivable, net	$ 120,119	$ 76,420	$ 117,975