Summary of Significant Accounting Policies - Summary of Revenue Disaggregated by Types and Geography (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 6,389	$ 1,584	$ 11,156	$ 3,530
Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	222	150	424	247
Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	4,657	1,400	8,111	2,972
Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,510	34	2,621	311
U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,312		1,333
U.S. [Member] | Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	28		49
U.S. [Member] | Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	875		875
U.S. [Member] | Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	409		409
Outside of U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	5,077	1,584	9,823	3,530
Outside of U.S. [Member] | Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	194	150	375	247
Outside of U.S. [Member] | Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3,782	1,400	7,236	2,972
Outside of U.S. [Member] | Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 1,101	$ 34	$ 2,212	$ 311