Summary of Change in Reserves for Discounts and Allowances (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	$ 51,503	$ 28,510
Provision	17,994	13,995
Payments/credits	(18,629)	(11,046)
Ending balance	50,868	31,459
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	588	1,378
Provision	2,435	2,566
Payments/credits	(2,336)	(3,049)
Ending balance	687	895
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	44,738	24,276
Provision	12,083	9,429
Payments/credits	(10,979)	(5,191)
Ending balance	45,842	28,514
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	1,506	538
Provision	1,373	936
Payments/credits	(1,291)	(791)
Ending balance	1,588	683
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	4,671	2,318
Provision	2,103	1,064
Payments/credits	(4,023)	(2,015)
Ending balance	$ 2,751	$ 1,367