Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	$ 28,510
Provision	13,995
Payments/credits	(11,046)
Balance, as of March 31, 2019	31,459
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	1,378
Provision	2,566
Payments/credits	(3,049)
Balance, as of March 31, 2019	895
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	24,276
Provision	9,429
Payments/credits	(5,191)
Balance, as of March 31, 2019	28,514
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	538
Provision	936
Payments/credits	(791)
Balance, as of March 31, 2019	683
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	2,318
Provision	1,064
Payments/credits	(2,015)
Balance, as of March 31, 2019	$ 1,367