Business Segment, Geographic, and Concentration Risk Information - Summary of Revenue by Geographical Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total revenue:
Total consolidated revenue	$ 14,873	$ 13,994	$ 4,595	$ 4,581	$ 5,113	$ 5,616	$ 5,193	$ 4,629	$ 38,043	$ 20,551	$ 13,944
United States
Total revenue:
Total consolidated revenue									19,933	3,573	3,270
India
Total revenue:
Total consolidated revenue									8,479	7,803	4,914
Austria
Total revenue:
Total consolidated revenue									3,962	5,197	2,323
China
Total revenue:
Total consolidated revenue									2,803	2,338	2,366
Taiwan
Total revenue:
Total consolidated revenue									500		84
Other Foreign Countries
Total revenue:
Total consolidated revenue									$ 2,366	$ 1,640	$ 987