Consolidated Statements of Changes in Stockholders' Equity - USD ($)
$ in Thousands
Common Stock
Additional Paid-in Capital
Accumulated Deficit
Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2013 $ 1 $ 94,798 $ (81,909) $ 12,890
Beginning Balance, (in shares) at Dec. 31, 2013 19,693,434      
Share-based compensation expense   2,730   2,730
Issuance of common stock in public offerings   7,770   7,770
Issuance of stock in public offering (in shares) 3,500,312      
Issuance of common stock for services   477   477
Issuance of common stock for services (in shares) 74,626      
Issuance of common stock upon cashless exercise of warrants (in shares) 6,903      
Issuance of common stock upon exercise of warrants   12   12
Issuance of common stock upon exercise of warrants (in shares) 9,975      
Issuance of common stock upon exercise of stock options   212   212
Issuance of common stock upon exercise of stock options (in shares) 132,900      
Issuance of common stock to 401(k) plan $ 173 173   173
Issuance of common stock to 401(k) plan (in shares) 41,753      
Net loss     (18,346) (18,346)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2014 $ 1 106,172 (100,255) 5,918
Ending Balance, (in shares) at Dec. 31, 2014 23,453,000      
Share-based compensation expense   4,666   4,666
Issuance of common stock in public offerings   14,480   14,480
Issuance of stock in public offering (in shares) 2,388,245      
Issuance of common stock upon cashless exercise of warrants (in shares) 25,052      
Issuance of common stock upon exercise of warrants   7,789   7,789
Issuance of common stock upon exercise of warrants (in shares) 1,379,575      
Issuance of common stock upon exercise of stock options   1,068   1,068
Issuance of common stock upon exercise of stock options (in shares) 316,177      
Fair value of derivative warrant liability reclassified to additional paid-in capital   16,121   16,121
Fractional shares issued due to reverse stock split 1,514      
Issuance of common stock to 401(k) plan $ 201 201   201
Issuance of common stock to 401(k) plan (in shares) 17,437      
Net loss     (33,314) (33,314)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2015 $ 1 150,497 (133,569) $ 16,929
Ending Balance, (in shares) at Dec. 31, 2015 27,555,948     27,555,948
Share-based compensation expense   5,063   $ 5,063
Issuance of common stock and warrants in public offerings, net of $2,040 issuance costs   29,905   29,905
Issuance of common stock and warrants in public offerings, net of $2,040 issuance costs (in shares) 4,293,333      
Issuance of common stock for services (in shares) 365      
Issuance of common stock upon cashless exercise of warrants (in shares) 4,979      
Issuance of common stock upon exercise of stock options   191   191
Issuance of common stock upon exercise of stock options (in shares) 135,205      
Issuance of common stock under ESPP   91   91
Issuance of common stock under ESPP (in shares) 16,729      
Issuance of common stock to 401(k) plan $ 208 208   208
Issuance of common stock to 401(k) plan (in shares) 37,528      
Net loss     (23,438) (23,438)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 31, 2016 $ 1 $ 185,955 $ (157,007) $ 28,949
Ending Balance, (in shares) at Dec. 31, 2016 32,044,087     32,044,087