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]
Total revenue	$ 5,422	$ 183	$ 16,578	$ 3,713
Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	237	173	662	421
Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	4,318		12,428	2,609
Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	867	10	3,488	683
U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	1,381		2,714
U.S. [Member] | Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	87		137
U.S. [Member] | Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	868		1,742
U.S. [Member] | Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	426		835
Outside of U.S. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	4,041	183	13,864	3,713
Outside of U.S. [Member] | Services [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	150	173	525	421
Outside of U.S. [Member] | Systems [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	3,450		10,686	2,609
Outside of U.S. [Member] | Instruments and Accessories [Member]
Disaggregation Of Revenue [Line Items]
Total revenue	$ 441	$ 10	$ 2,653	$ 683