Revenue Recognition - Summary of Receivables and Contract Liabilities From Contracts with Customers (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Change In Contract With Customer Liability [Abstract]
Accounts receivable, gross	$ 37,210	$ 26,061
Chargebacks and other deductions	(19,909)	(13,101)
Allowance for doubtful accounts	(133)	(9)
Accounts receivable, net	17,168	12,951
Deferred revenue	20,071	190
Total contract liabilities	$ 20,071	$ 190