Summary of Significant Accounting Policies - Summary of Product Revenue Allowance And Reserve Categories (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Service Fees, Allowances and Chargebacks [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	$ 1,049	$ 1,010	$ 601	$ 238	$ 152	$ 60
Provision related to sales in the current quarter	1,845	1,196	741	516	300	186
Credits and payments made	(1,229)	(1,157)	(332)	(298)	(214)	(94)
Ending Balance	1,665	1,049	1,010	456	238	152
Government Rebates and Other Incentives [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	535	479	491	148	64	15
Provision related to sales in the current quarter	127	121	24	158	84	49
Credits and payments made	(117)	(65)	(36)	(6)
Adjustments related to prior period sales	(159)
Ending Balance	386	535	479	300	148	64
Product Returns [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	235	149	125	36	14	2
Provision related to sales in the current quarter	136	92	57	38	22	12
Credits and payments made	(6)	(6)	(33)
Ending Balance	365	235	149	74	36	14
Provider Rebates [Member]
Summary Of Significant Accounting Policies [Line Items]
Provision related to sales in the current quarter	1,715
Ending Balance	1,715
Product Revenue Allowance and Reserve [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	1,819	1,638	1,217	422	230	77
Provision related to sales in the current quarter	3,823	1,409	822	712	406	247
Credits and payments made	(1,352)	(1,228)	(401)	(304)	(214)	(94)
Adjustments related to prior period sales	(159)
Ending Balance	$ 4,131	$ 1,819	$ 1,638	$ 830	$ 422	$ 230