Summary of Significant Accounting Policies - Summary of Product Revenue Allowance And Reserve Categories (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Trade Discounts, Allowances and Government Chargebacks [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	$ 601	$ 60
Provision related to sales in the current year	741	186
Credits and payments made	(332)	(94)
Ending Balance	1,010	152
Government Rebates and Other Incentives [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	491	15
Provision related to sales in the current year	24	49
Credits and payments made	(36)
Ending Balance	479	64
Returns [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	125	2
Provision related to sales in the current year	57	12
Credits and payments made	(33)
Ending Balance	149	14
Product Revenue Allowance and Reserve [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	1,217	77
Provision related to sales in the current year	822	247
Credits and payments made	(401)	(94)
Ending Balance	$ 1,638	$ 230