Trade Accounts Receivable, Net (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Trade Accounts Receivable, Net
Trade accounts receivable	$ 130,612	$ 85,732	$ 123,531
Allowance for doubtful accounts	(1,141)	(1,288)	(1,343)
Allowance for sales discounts and returns	(2,583)	(1,632)	(2,069)
Trade accounts receivable, net	$ 126,888	$ 82,812	$ 120,119