Accounts Receivable, Sales and Allowances - Net Trade Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Gross accounts receivable	$ 382,606	$ 378,759
Less reserves for:
Chargebacks	(64,698)	(73,984)
Rebates	(86,468)	(111,945)
Product returns	(41,213)	(41,687)
Discounts and allowances	(10,579)	(7,779)
Advertising and promotions	(1,758)	(1,301)
Doubtful accounts	(837)	(680)
Trade accounts receivable, net	$ 177,053	$ 141,383