Accounts Receivable and Reserves for Product Sales - Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2016	$ 306
Provision	15,876
Payments/credits	(7,595)
Balance, as of December 31, 2017	8,587
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2016	1
Provision	6,455
Payments/credits	(5,461)
Balance, as of December 31, 2017	995
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2016	238
Provision	7,659
Payments/credits	(938)
Balance, as of December 31, 2017	6,959
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Provision	469
Payments/credits	(300)
Balance, as of December 31, 2017	169
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2016	67
Provision	1,293
Payments/credits	(896)
Balance, as of December 31, 2017	$ 464