Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	$ 28,510
Provision	50,871
Payments/credits	(38,875)
Balance, as of September 30, 2019	40,506
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	1,378
Provision	7,291
Payments/credits	(7,838)
Balance, as of September 30, 2019	831
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	24,276
Provision	32,310
Payments/credits	(22,053)
Balance, as of September 30, 2019	34,533
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	538
Provision	3,541
Payments/credits	(3,009)
Balance, as of September 30, 2019	1,070
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	2,318
Provision	7,729
Payments/credits	(5,975)
Balance, as of September 30, 2019	$ 4,072