Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	$ 8,587
Provision	21,222
Payments/credits	(11,330)
Balance, as of June 30, 2018	18,479
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	995
Provision	6,490
Payments/credits	(6,622)
Balance, as of June 30, 2018	863
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	6,959
Provision	11,178
Payments/credits	(1,978)
Balance, as of June 30, 2018	16,159
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	169
Provision	1,094
Payments/credits	(917)
Balance, as of June 30, 2018	346
Other [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2017	464
Provision	2,460
Payments/credits	(1,813)
Balance, as of June 30, 2018	$ 1,111