Summarize Activity of the Net Product Revenue Allowance and Reserve Categories (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	$ 27,198	$ 15,796
Provision related to current period sales	178,531	104,601
Provision related to prior period sales	(1,075)	(537)
Credits/payments made for current period sales	(132,385)	(77,747)
Credits/payments made for prior period sales	(24,176)	(14,915)
Ending balance	48,093	27,198
Trade Allowances
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	3,743	4,296
Provision related to current period sales	35,067	22,952
Provision related to prior period sales	(323)	(87)
Credits/payments made for current period sales	(23,087)	(19,213)
Credits/payments made for prior period sales	(3,365)	(4,205)
Ending balance	12,035	3,743
Rebates, Chargebacks and Discounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	20,915	9,881
Provision related to current period sales	126,903	69,370
Provision related to prior period sales	(682)	(450)
Credits/payments made for current period sales	(96,181)	(48,719)
Credits/payments made for prior period sales	(18,891)	(9,167)
Ending balance	32,064	20,915
Product Returns
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	859	535
Provision related to current period sales	1,480	583
Credits/payments made for current period sales	(344)
Credits/payments made for prior period sales	(108)	(259)
Ending balance	1,887	859
Other Incentives
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning balance	1,681	1,084
Provision related to current period sales	15,081	11,696
Provision related to prior period sales	(70)
Credits/payments made for current period sales	(12,773)	(9,815)
Credits/payments made for prior period sales	(1,812)	(1,284)
Ending balance	$ 2,107	$ 1,681