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 - Status of Our Stock Options (Detail)

v3.8.0.1
Stock Options, Stock Purchase Plan and Warrants - Status of Our Stock Options (Detail) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Stock options, beginning balance 5,136,110 5,326,505 4,012,096
Stock options, granted 2,119,498 2,617,526 1,819,000
Stock options, exercised (565,569) (2,483,519) (492,091)
Stock options, cancelled (347,513) (324,402) (12,500)
Stock options, ending balance 6,342,526 5,136,110 5,326,505
Stock options, exercisable, ending balance 2,103,342    
Weighted average exercise price, beginning balance $ 5.76 $ 3.07 $ 2.04
Weighted average exercise price, granted 7.60 7.14 4.90
Weighted average exercise price, exercised 3.84 1.69 1.45
Weighted average exercise price, cancelled 6.12 3.99 3.19
Weighted average exercise price, ending balance 6.51 $ 5.76 $ 3.07
Weighted average exercise price, exercisable, ending balance $ 5.50