Summary of Change in Reserves for Discounts and Allowances (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	$ 51,503	$ 28,510
Provision	58,545	50,871
Payments/credits	(58,230)	(38,875)
Ending balance	51,818	40,506
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	588	1,378
Provision	7,137	7,291
Payments/credits	(6,699)	(7,838)
Ending balance	1,026	831
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	44,738	24,276
Provision	38,763	32,310
Payments/credits	(39,489)	(22,053)
Ending balance	44,012	34,533
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	1,506	538
Provision	4,599	3,541
Payments/credits	(4,348)	(3,009)
Ending balance	1,757	1,070
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	4,671	2,318
Provision	8,046	7,729
Payments/credits	(7,694)	(5,975)
Ending balance	$ 5,023	$ 4,072