Trade Accounts Receivable, Net (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Trade Accounts Receivable, Net
Trade accounts receivable	$ 117,728	$ 92,413	$ 105,880
Allowance for doubtful accounts	(870)	(945)	(1,134)
Allowance for sales discounts and returns	(2,699)	(1,451)	(1,933)
Trade accounts receivable, net	$ 114,159	$ 90,017	$ 102,813