Segment, Customer and Geographic Information - Revenue by Geographical Location (Detail) - USD ($) $ 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
Revenue, Major Customer [Line Items]
Revenue									$ 93,774	$ 76,051	$ 51,326
Product
Revenue, Major Customer [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
Product | UNITED STATES
Revenue, Major Customer [Line Items]
Revenue									20,611	12,563	6,316
Product | FRANCE
Revenue, Major Customer [Line Items]
Revenue									20,075	23,043	9,692
Product | BELGIUM
Revenue, Major Customer [Line Items]
Revenue									7,272	6,788	6,263
Product | Other Countries
Revenue, Major Customer [Line Items]
Revenue									26,691	18,514	21,297
Government Contract
Revenue, Major Customer [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
Government Contract | UNITED STATES
Revenue, Major Customer [Line Items]
Revenue									$ 19,125	$ 15,143	$ 7,758