Quarterly results of operations (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	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
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 49,652	$ 50,781	$ 44,759	$ 35,309	$ 48,880	$ 47,822	$ 42,686	$ 40,242	$ 180,501	$ 179,630	$ 165,989
Gross Profit	30,510	31,888	27,016	19,685	31,197	31,138	25,651	23,901	109,099	111,887	101,062
Net loss	(1,686)	298	(4,857)	(11,735)	(1,101)	(249)	(3,554)	(4,770)	$ (17,980)	$ (9,674)	$ (10,897)
Net Income (Loss) Available to Common Stockholders, Basic	$ (1,686)	$ 298	$ (4,857)	$ (11,735)	$ (1,101)	$ (249)	$ (3,554)	$ (4,770)
Earnings Per Share, Basic	$ (0.05)	$ 0.01	$ (0.16)	$ (0.38)
Basic and diluted					$ (0.04)	$ (0.01)	$ (0.26)	$ (0.24)	$ (0.57)	$ (0.32)	$ (0.38)
Earnings Per Share, Diluted	$ (0.05)	$ 0.01	$ (0.16)	$ (0.38)
Basic	31,579	31,459	31,242	30,800					31,273	30,041	28,655
Weighted Average Number of Shares Outstanding, Basic					30,592	29,861	29,867	29,476
Diluted	31,579	31,944	31,242	30,800					31,273	30,041	28,655