Annual report pursuant to Section 13 and 15(d)

Stock Incentive Plan - Non-vested Share-based Activity (Details)

v3.8.0.1
Stock Incentive Plan - Non-vested Share-based Activity (Details) - Employee Consultants and Directors Stock Options [Member] - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Non-vested share-based payment activity with employees      
Number of non-vested options outstanding at the beginning of the period (in shares) 2,121,319 1,179,969 1,159,486
Number of non-vested options granted (in shares) 1,298,355 1,529,850 946,250
Number of options vested (in shares) (692,253) (512,562) (635,289)
Number of non-vested options forfeited (in shares) (94,777) (75,938) (290,478)
Number of non-vested options outstanding at the end of the period (in shares) 2,632,644 2,121,319 1,179,969
Weighted average grant-date fair value of non-vested options outstanding at the beginning of the period (in dollars per share) $ 6.72 $ 4.21 $ 3.37
Weighted average grant-date fair value of options granted (in dollars per share) 19.99 7.67 4.31
Weighted average grant-date fair value of options vested (in dollars per share) (6.49) (4.21) (3.32)
Weighted average grant-date fair value of non-vested options forfeited (in dollars per share) (6.29) (3.74) (3.12)
Weighted average grant-date fair value of non-vested options outstanding at the end of the period (in dollars per share) $ 13.33 $ 6.72 $ 4.21