Supplementary Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 31,335	$ 22,484	$ 19,011	$ 18,027	$ 14,260	$ 16,953	$ 9,361	$ 23,350	$ 90,857	$ 63,924	$ 54,383
Gross profit	22,706	14,346	11,284	10,361	7,074	9,283	2,252	14,961	58,697	33,570	26,076
Profit (loss) from operations	5,995	(1,336)	(4,246)	(4,322)	(4,031)	(2,521)	(9,623)	1,191	(3,909)	(14,984)	(19,245)
Net loss	$ 5,242	$ (1,069)	$ (4,651)	$ (7,659)	$ (5,407)	$ (2,388)	$ (9,778)	$ 287	$ (8,137)	$ (17,286)	$ (19,566)
Net (loss) profit per share (Basic) (in USD per share)	$ 0.12								$ (0.20)
Net (loss) profit per share (Diluted) (in USD per share)	$ 0.11	$ (0.02)	$ (0.12)	$ (0.21)					$ (0.20)
Net (loss) profit per share (Basic and Diluted) (in dollars per share)					$ (0.16)	$ (0.07)	$ (0.31)	$ 0.01		$ (0.52)	$ (1.18)