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Revenue Recognition - Topic 606 (Narrative) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
REVENUE RECOGNITION - TOPIC 606
Revenues	$ 18,063,000	$ 16,683,000	$ 15,854,000	$ 14,120,000	$ 13,176,000	$ 11,828,000	$ 16,409,000	$ 11,920,000	$ 64,720,000	$ 53,333,000
Net income	$ 1,193,000	$ 1,067,000	$ 740,000	$ (173,000)	$ 503,000	$ (72,000)	$ 1,095,000	$ (214,000)	2,827,000	$ 1,312,000
Amounts reclassified from beginning contract liabilities to revenue									354,000
Effect of adoption of Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member]
REVENUE RECOGNITION - TOPIC 606
Revenues									81,000
Net income									$ 64,000
Income per share									$ 0.01
Impairment losses for contract assets									$ 0
Effect of adoption of Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member] \| Minimum [Member]
REVENUE RECOGNITION - TOPIC 606
Period over which unsatisfied performance obligations are expected to be recognized as revenue	1 year								1 year
Effect of adoption of Topic 606 [Member] \| Accounting Standards Update 2014-09 [Member] \| Maximum [Member]
REVENUE RECOGNITION - TOPIC 606
Period over which unsatisfied performance obligations are expected to be recognized as revenue	3 years								3 years