Statement of Stockholders’ Equity (Unaudited) - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total
Balance (in shares) at Dec. 31, 2017	62,310,795				62,310,795
Balance at Dec. 31, 2017	$ 62	$ 392,103	$ (357,490)	$ (42)	$ 34,633
Increase (Decrease) in Stockholders' Equity
Stock-based compensation expense		1,498			1,498
Exercise of stock options		57			$ 57
Exercise of stock options (in shares)	88,048				88,048
Issuance of common stock, net of issuance costs	$ 6	9,148			$ 9,154
Issuance of common stock, net of issuance costs (in shares)	5,204,893
Unrealized loss on marketable securities				(4)	(4)
Net loss			(9,021)		$ (9,021)
Balance (in shares) at Mar. 31, 2018	67,603,736				67,603,736
Balance at Mar. 31, 2018	$ 68	$ 402,806	$ (366,511)	$ (46)	$ 36,317