Summary of Change in Reserves for Discounts and Allowances (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	$ 51,503	$ 28,510
Provision	37,445	30,351
Payments/credits	(40,559)	(24,477)
Ending balance	48,389	34,384
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	588	1,378
Provision	4,480	4,874
Payments/credits	(4,427)	(4,712)
Ending balance	641	1,540
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	44,738	24,276
Provision	25,664	21,004
Payments/credits	(27,617)	(15,002)
Ending balance	42,785	30,278
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	1,506	538
Provision	2,952	2,240
Payments/credits	(2,796)	(1,909)
Ending balance	1,662	869
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	4,671	2,318
Provision	4,349	2,233
Payments/credits	(5,719)	(2,854)
Ending balance	$ 3,301	$ 1,697