Summary of Significant Accounting Policies - Summary of Revenue Disaggregated by Types and Geography (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 4,767	$ 1,946
Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3,454	1,572
Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,111	277
Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	202	97
U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	21
U.S. [Member] | Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	21
Outside of U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	4,746	1,946
Outside of U.S. [Member] | Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3,454	1,572
Outside of U.S. [Member] | Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,111	277
Outside of U.S. [Member] | Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 181	$ 97