Summary of Significant Accounting Policies - Summary of Revenue Disaggregated by Type and Geography (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 600	$ 2,181
Systems
Disaggregation of Revenue [Line Items]
Total revenue	69	1,283
Instruments and accessories
Disaggregation of Revenue [Line Items]
Total revenue	173	546
Services
Disaggregation of Revenue [Line Items]
Total revenue	358	352
U.S.
Disaggregation of Revenue [Line Items]
Total revenue	159	133
U.S. | Systems
Disaggregation of Revenue [Line Items]
Total revenue	30	0
U.S. | Instruments and accessories
Disaggregation of Revenue [Line Items]
Total revenue	60	0
U.S. | Services
Disaggregation of Revenue [Line Items]
Total revenue	69	133
Outside of U.S.
Disaggregation of Revenue [Line Items]
Total revenue	441	2,048
Outside of U.S. | Systems
Disaggregation of Revenue [Line Items]
Total revenue	39	1,283
Outside of U.S. | Instruments and accessories
Disaggregation of Revenue [Line Items]
Total revenue	113	546
Outside of U.S. | Services
Disaggregation of Revenue [Line Items]
Total revenue	$ 289	$ 219