Annual report pursuant to Section 13 and 15(d)

Stock Options - Non-vested Share-based Activity (Details)

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Stock Options - Non-vested Share-based Activity (Details) - Employee Consultants and Directors Stock Options [Member] - $ / shares
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Non-vested share-based payment activity with employees      
Number of non-vested options outstanding at the beginning of the period (in shares) 1,159,486 675,196  
Number of non-vested options granted (in shares) 946,250 935,750 935,750
Number of options vested (in shares) (635,289) (407,437)  
Number of non-vested options forfeited (in shares) (290,478) (44,023)  
Number of non-vested options outstanding at the end of the period (in shares) 1,179,969 1,159,486 675,196
Weighted average grant-date fair value of non-vested options outstanding at the beginning of the period (in dollars per share) $ 3.37 $ 2.88  
Weighted average grant-date fair value of options granted (in dollars per share) 4.31 3.57  
Weighted average grant-date fair value of options vested (in dollars per share) (3.32) (3.03)  
Weighted average grant-date fair value of non-vested options forfeited (in dollars per share) (3.12) (3.78)  
Weighted average grant-date fair value of non-vested options outstanding at the end of the period (in dollars per share) $ 4.21 $ 3.37 $ 2.88