Revenue Recognition and Accounts Receivable - Schedule of Net Sales (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue Recognition [Abstract]
Product sales									$ 395,589	$ 373,538	$ 355,652
Marketing service fees									57,453	60,285	54,136
Net sales	$ 121,078	$ 111,708	$ 111,547	$ 108,709	$ 116,896	$ 105,247	$ 108,942	$ 102,738	$ 453,042	$ 433,823	$ 409,788