Summary of Significant Accounting Policies - Summary of Product Revenue Allowance And Reserve Categories (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018
Trade Discounts, Allowances and Government Chargebacks [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	$ 1,010	$ 601	$ 152	$ 60
Provision related to sales in the current quarter	1,196	741	300	186
Credits and payments made	(1,157)	(332)	(214)	(94)
Ending Balance	1,049	1,010	238	152
Government Rebates and Other Incentives [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	479	491	64	15
Provision related to sales in the current quarter	121	24	84	49
Credits and payments made	(65)	(36)
Ending Balance	535	479	148	64
Returns [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	149	125	14	2
Provision related to sales in the current quarter	92	57	22	12
Credits and payments made	(6)	(33)
Ending Balance	235	149	36	14
Product Revenue Allowance and Reserve [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	1,638	1,217	230	77
Provision related to sales in the current quarter	1,409	822	406	247
Credits and payments made	(1,228)	(401)	(214)	(94)
Ending Balance	$ 1,819	$ 1,638	$ 422	$ 230