Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	$ 8,587
Provision	48,614
Payments/credits	(28,691)
Balance, as of December 31, 2018	28,510
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	995
Provision	12,284
Payments/credits	(11,901)
Balance, as of December 31, 2018	1,378
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	6,959
Provision	28,420
Payments/credits	(11,103)
Balance, as of December 31, 2018	24,276
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	169
Provision	2,624
Payments/credits	(2,255)
Balance, as of December 31, 2018	538
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	464
Provision	5,286
Payments/credits	(3,432)
Balance, as of December 31, 2018	$ 2,318