Summary of Change in Reserves for Discounts and Allowances (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	$ 50,970	$ 51,503
Provision	22,027	17,994
Payments/credits	(17,128)	(18,629)
Ending balance	55,869	50,868
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	2,281	588
Provision	2,085	2,435
Payments/credits	(3,969)	(2,336)
Ending balance	397	687
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	41,771	44,738
Provision	14,907	12,083
Payments/credits	(9,108)	(10,979)
Ending balance	47,570	45,842
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	1,949	1,506
Provision	1,844	1,373
Payments/credits	(1,432)	(1,291)
Ending balance	2,361	1,588
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	4,969	4,671
Provision	3,191	2,103
Payments/credits	(2,619)	(4,023)
Ending balance	$ 5,541	$ 2,751