Total Net Sales Based on Disaggregation Criteria (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 net sales	$ 20,022	$ 15,432	$ 56,844	$ 43,664
Point-in-Time
Disaggregation Of Revenue [Line Items]
Total net sales	18,850	15,101	53,728	42,637
Over Time
Disaggregation Of Revenue [Line Items]
Total net sales	1,172	331	3,116	1,027
Americas
Disaggregation Of Revenue [Line Items]
Total net sales	15,035	10,291	44,172	28,894
Americas | Point-in-Time
Disaggregation Of Revenue [Line Items]
Total net sales	13,930	9,960	41,150	27,893
Americas | Over Time
Disaggregation Of Revenue [Line Items]
Total net sales	1,105	331	3,022	1,001
Europe and the Middle East
Disaggregation Of Revenue [Line Items]
Total net sales	2,161	1,771	6,992	5,767
Europe and the Middle East | Point-in-Time
Disaggregation Of Revenue [Line Items]
Total net sales	2,117	1,771	6,921	5,741
Europe and the Middle East | Over Time
Disaggregation Of Revenue [Line Items]
Total net sales	44		71	26
Asia-Pacific
Disaggregation Of Revenue [Line Items]
Total net sales	2,826	3,370	5,680	9,003
Asia-Pacific | Point-in-Time
Disaggregation Of Revenue [Line Items]
Total net sales	2,803	$ 3,370	5,657	$ 9,003
Asia-Pacific | Over Time
Disaggregation Of Revenue [Line Items]
Total net sales	$ 23		$ 23