Earnings Per Share (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	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Calculation of basic and diluted loss per share [Abstract]
Net loss	$ (6,417)	$ (4,934)	$ (6,450)	$ (7,605)	$ (6,034)	$ (3,552)	$ (3,798)	$ (3,894)	$ (25,406)	$ (17,278)	$ (28,569)
Basic and diluted weighted average number of shares outstanding (in shares)									62,985,763	58,354,397	55,984,825
Basic and diluted loss per share (in dollars per share)	$ (0.09)	$ (0.08)	$ (0.10)	$ (0.13)	$ (0.10)	$ (0.06)	$ (0.07)	$ (0.07)	$ (0.40)	$ (0.30)	$ (0.51)