Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Allowance For Credit Loss [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 104	$ 63
Charged to Costs and Expenses	161	63
Addition (Deductions)	(152)	(22)
Balance at End of Year	113	104
Warranty Reserves [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	444	339
Charged to Costs and Expenses	(203)	213
Addition (Deductions)	44	(108)
Balance at End of Year	285	444
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	13,490	14,457
Charged to Costs and Expenses	0	0
Addition (Deductions)	(552)	(967)
Balance at End of Year	$ 12,938	$ 13,490