Other Income (Expense), Net - Components of Other Income (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Income and Expenses [Abstract]
Rental income	$ 792,000	$ 792,000	$ 792,000
Interest income	300,000	257,000	124,000
Foreign currency losses, net	(108,000)	(260,000)	323,000
Gain on disposal of equipment	38,000	57,000	14,000
Credit gains on available-for-sale securities	4,000	7,000	11,000
Other	40,000	21,000	(2,000)
Total other income (expense), net	$ 1,066,000	$ 874,000	$ 1,262,000