Schedule II - Valuation and Qualifying Accounts - Valuation and Qualifying Accounts and Reserves (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Doubtful Receivables [Member]
Balance at beginning of period		$ 117,000	$ 267,000
Charged (credited) to costs & expenses		71,000	91,000
Deductions	[1]	92,000	241,000
Balance at end of period		96,000	117,000
Discount Returns and Allowance [Member]
Balance at beginning of period		155,000	137,000
Charged (credited) to costs & expenses	[2]	(48,000)	18,000
Deductions
Balance at end of period		107,000	155,000
Doubtful Receivables & Discounts Returns and Allowances [Member]
Balance at beginning of period		272	404
Charged (credited) to costs & expenses		23	109
Deductions		92	241
Balance at end of period		203	272
Valuation Allowance of Deferred Tax Assets [Member]
Balance at beginning of period		12,588,000	19,194,000
Charged (credited) to costs & expenses
Deductions		2,857,000	6,606,000
Balance at end of period		$ 9,731,000	$ 12,588,000

[1] Uncollectible receivables written-off, net of recoveries.

[2] Represents net increase (decrease) in the reserve.