Selected Quarterly Information (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 34,775,000	$ 31,678,000	$ 31,932,000	$ 31,574,000	$ 34,789,000	$ 32,324,000	$ 32,660,000	$ 31,445,000	$ 129,959,000	$ 131,218,000	$ 122,535,000
Gross profit	27,643,000	24,427,000	24,836,000	24,045,000	27,222,000	24,718,000	25,685,000	24,092,000	100,951,000	101,717,000	93,433,000
Income (loss) from operations	5,735,000	1,781,000	(1,414,000)	(2,300,000)	620,000	(2,241,000)	(2,734,000)	(3,151,000)	3,802,000	(7,506,000)	(16,578,000)
Net income (loss)	$ 5,420,000	$ 1,729,000	$ (1,338,000)	$ (2,329,000)	$ 607,000	$ (2,287,000)	$ (2,764,000)	$ (3,157,000)	$ 3,482,000	$ (7,601,000)	$ (16,557,000)	$ (16,557,000)
Net (loss) income per share:
Basic (in dollars per share)	$ 0.19	$ 0.06	$ (0.05)	$ (0.08)	$ 0.02	$ (0.08)	$ (0.10)	$ (0.12)	$ 0.12	$ (0.28)	$ (0.63)
Diluted (in dollars per share)	$ 0.19	$ 0.06	$ (0.05)	$ (0.08)	$ (0.12)	$ (0.10)	$ (0.08)	$ 0.02	$ 0.12	$ (0.28)	$ (0.63)