Annual report pursuant to Section 13 and 15(d)

Annual report pursuant to Section 13 and 15(d)

Stock Options, Stock Purchase Plan and Warrants - Roll Forward of Non-Vested Stock Options Activity (Detail)

v3.8.0.1
Stock Options, Stock Purchase Plan and Warrants - Roll Forward of Non-Vested Stock Options Activity (Detail) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Number of Options, Non-vested, Beginning balance 4,008,478    
Number of Options, Granted 2,119,498 2,617,526 1,819,000
Number of Options, Vested (1,584,554)    
Number of Options, Forfeited (304,237)    
Number of Options, Non-vested, Ending balance 4,239,185 4,008,478  
Weighted average grant date fair value, Non-vested, Beginning balance $ 2.09    
Weighted average grant date fair value, Granted 2.26    
Weighted average grant date fair value, Vested 2.20    
Weighted average grant date fair value, Forfeited 2.38    
Weighted average grant date fair value, Non-vested, Ending balance $ 2.29 $ 2.09