CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Total
Beginning Balance at Dec. 31, 2015	$ 300	$ 111,369	$ (103,473)	$ 8,196
Beginning Balance (in shares) at Dec. 31, 2015	29,985,000
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		1,390		1,390
Exercise of stock options	$ 3	1,075		1,078
Exercise of stock options (in shares)	341,000
Issuance of common shares	$ 27	18,641		18,668
Issuance of common shares (in shares)	2,683,000
Net loss			(14,411)	(14,411)
Ending Balance at Dec. 31, 2016	$ 330	132,475	(117,884)	14,921
Ending Balance (in shares) at Dec. 31, 2016	33,009,000
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		3,609		3,609
Exercise of stock options	$ 5	1,429		1,434
Exercise of stock options (in shares)	536,000
Issuance of common shares	$ 8	15,655		15,663
Issuance of common shares (in shares)	805,000
Net loss			(10,445)	(10,445)
Ending Balance at Dec. 31, 2017	$ 343	153,168	(128,329)	$ 25,182
Ending Balance (in shares) at Dec. 31, 2017	34,350,000			34,350,329
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		7,606		$ 7,606
Exercise of stock options and employee stock purchase plan	$ 11	3,873		3,884
Exercise of stock options and employee stock purchase plan (in shares)	1,101,000
Issuance of common shares	$ 35	132,672		132,707
Issuance of common shares (in shares)	3,450,000
Net loss			(22,397)	(22,397)
Ending Balance at Dec. 31, 2018	$ 389	$ 297,319	$ (150,726)	$ 146,982
Ending Balance (in shares) at Dec. 31, 2018	38,901,000			38,900,875