Annual report pursuant to Section 13 and 15(d)

Loss Per Share - Narrative (Details)

v3.8.0.1
Loss Per Share - Narrative (Details) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Number of common stock warrant and common stock options exercised (in shares) 1,720,649 3,420,697 25,686,153
Number of common stock issued for stock warrant and stock options exercised (in shares) 1,447,792 3,292,753 24,466,106
Shares surrendered in lieu of cash payment (in shares) 272,857 127,944 1,220,047
Common stock investments, available for sale      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Potential common shares excluded from diluted net loss per share calculation (in shares) 6,255,624 9,494,999 14,269,717