Annual report pursuant to Section 13 and 15(d)

Equity - Summary of Unvested Shares of Restricted Common Stock (Detail)

v3.8.0.1
Equity - Summary of Unvested Shares of Restricted Common Stock (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted Incentive [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Beginning Balance, Restricted Shares of Common Stock/Units 1,181,672 1,248,069 964,820
Granted, Restricted Shares of Common Stock/Units 452,864 661,055 586,648
Vested, Restricted Shares of Common Stock/Units (230,424) (716,264) (285,289)
Forfeited, Restricted Shares of Common Stock/Units (4,519) (11,188) (18,110)
Ending Balance, Restricted Shares of Common Stock/Units 1,399,593 1,181,672 1,248,069
Beginning Balance, Weighted Average Share Price $ 17.76 $ 15.16 $ 13.41
Granted, Weighted Average Share Price 19.06 18.62 17.29
Vested, Weighted Average Share Price 14.41 14.03 13.61
Forfeited, Weighted Average Share Price 18.72 17.25 15.54
Ending Balance, Weighted Average Share Price $ 18.73 $ 17.76 $ 15.16
Beginning Balance, Fair Value of Restricted Shares of Common Stock $ 21.0 $ 18.9 $ 12.9
Granted, Fair Value of Restricted Shares of Common Stock 8.6 12.3 10.2
Vested, Fair Value of Restricted Shares of Common Stock (3.3) (10.0) (3.9)
Forfeited, Fair Value of Restricted Shares of Common Stock (0.1) (0.2) (0.3)
Ending Balance, Fair Value of Restricted Shares of Common Stock $ 26.2 $ 21.0 $ 18.9
Restricted stock and restricted stock units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted, Restricted Shares of Common Stock/Units 257,284    
Vested, Restricted Shares of Common Stock/Units (376)    
Forfeited, Restricted Shares of Common Stock/Units (1,202)    
Ending Balance, Restricted Shares of Common Stock/Units 255,706    
Granted, Weighted Average Share Price $ 18.99    
Vested, Weighted Average Share Price 18.99    
Forfeited, Weighted Average Share Price 18.99    
Ending Balance, Weighted Average Share Price $ 18.99    
Granted, Fair Value of Restricted Shares of Common Stock $ 4.9    
Ending Balance, Fair Value of Restricted Shares of Common Stock $ 4.9