Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information [Line Items]
Revenue									$ 93,774	$ 76,051	$ 51,326
Gross profit	$ 11,624	$ 10,436	$ 10,098	$ 9,072	$ 8,083	$ 7,257	$ 7,700	$ 6,234	41,230	29,274	21,037
Net loss	$ (16,923)	$ (17,967)	$ (17,562)	$ (18,792)	$ (16,205)	$ (14,192)	$ (13,282)	$ (13,885)	(71,244)	(57,564)	(60,585)
Basic	$ (0.12)	$ (0.13)	$ (0.13)	$ (0.14)	$ (0.12)	$ (0.11)	$ (0.10)	$ (0.11)
Diluted	$ (0.12)	$ (0.13)	$ (0.13)	$ (0.14)	$ (0.12)	$ (0.11)	$ (0.10)	$ (0.11)
Product
Quarterly Financial Information [Line Items]
Revenue	$ 20,917	$ 18,019	$ 18,209	$ 17,504	$ 16,525	$ 15,399	$ 15,420	$ 13,564	74,649	60,908	43,568
Government Contract
Quarterly Financial Information [Line Items]
Revenue	$ 5,571	$ 4,827	$ 4,266	$ 4,461	$ 3,713	$ 3,928	$ 4,047	$ 3,455	$ 19,125	$ 15,143	$ 7,758