Trade Accounts Receivable, Net (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Trade Accounts Receivable, Net
Trade accounts receivable	$ 122,328	$ 85,732	$ 111,726
Allowance for doubtful accounts	(1,384)	(1,288)	(1,514)
Allowance for sales discounts and returns	(2,049)	(1,632)	(1,787)
Trade accounts receivable, net	$ 118,895	$ 82,812	$ 108,425