Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 113	$ 104
Charged to Costs and Expenses	0	161
Addition (Deductions)	(49)	(152)
Balance at End of Year	64	113
Warranty Reserves [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	285	444
Charged to Costs and Expenses	(95)	(203)
Addition (Deductions)	67	44
Balance at End of Year	257	285
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	12,938	13,490
Charged to Costs and Expenses	0	0
Addition (Deductions)	2,320	(552)
Balance at End of Year	$ 15,258	$ 12,938