Schedule II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts [Member] - USD ($)		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 224,000	$ 159,000	$ 153,000
Charge (Recovery) to Costs and Expenses		(144,000)	65,000	6,000
Other Charges, Deductions	[1]	(21,000)
Balance at End of Period		$ 59,000	$ 224,000	$ 159,000

[1] Reflects uncollectible accounts written off, net of recoveries.