Summary of Significant Accounting Policies - Summary of Revenue Disaggregated by Types and Geography (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	$ 17,666	$ 12,197	$ 60,299	$ 14,122
Product
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	16,492	11,358	57,237	11,358
Service
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	1,056	721	2,706	2,408
Distribution Rights
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	118	118	356	356
U.S.
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	6,753	6,127	27,239	7,318
U.S. | Product
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	6,187	5,739	25,775	5,739
U.S. | Service
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	566	388	1,464	1,579
Outside of U.S. ("OUS")
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	10,913	6,070	33,060	6,804
Outside of U.S. ("OUS") | Product
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	10,305	5,619	31,462	5,619
Outside of U.S. ("OUS") | Service
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	490	333	1,242	829
Outside of U.S. ("OUS") | Distribution Rights
Disaggregation Of Revenue [Line Items]
Product, service and distribution rights revenue	$ 118	$ 118	$ 356	$ 356