Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Restricted Stock Activity (Detail)

v3.8.0.1
Stockholders' Equity - Restricted Stock Activity (Detail) - Restricted Stock [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Number of shares, Unvested balance 10,094,095 8,757,935
Number of shares, Restricted stock granted 1,325,396 1,240,868
Number of shares, Restricted stock cancelled   (33,333)
Number of shares, Restricted stock vested (213,333) (173,333)
Number of shares, Restricted stock units granted 1,128,750 641,000
Number of shares, Forfeited (15,000) (111,750)
Restricted stock units vested (445,874) (227,292)
Number of shares, Unvested balance 11,874,034 10,094,095
Weighted average grant price, Unvested balance $ 2.49 $ 2.47
Weighted average grant price, Restricted stock granted 2.70 2.77
Weighted average grant price, Restricted stock cancelled   2.69
Weighted average grant price, Restricted stock vested 2.75 2.73
Weighted average grant price, Restricted stock units granted 4.17 2.93
Weighted average grant price, Restricted stock units cancelled 2.98 3.58
Weighted average grant price, Restricted stock units vested 3.50 3.56
Weighted average grant price, Unvested balance $ 2.63 $ 2.49