Accounts Receivable and Reserves for Product Sales - Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	$ 8,587
Provision	9,978
Payments/credits	(4,486)
Balance, as of March 31, 2018	14,079
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	995
Provision	2,790
Payments/credits	(2,916)
Balance, as of March 31, 2018	869
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	6,959
Provision	5,159
Payments/credits	(989)
Balance, as of March 31, 2018	11,129
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	169
Provision	495
Payments/credits	(435)
Balance, as of March 31, 2018	229
Other [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	464
Provision	1,534
Payments/credits	(146)
Balance, as of March 31, 2018	$ 1,852