Quarterly report pursuant to Section 13 or 15(d)

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

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Equity - Summary of Unvested Shares of Restricted Common Stock (Detail) - Restricted Incentive [Member] - USD ($)
$ / shares in Units, $ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Beginning Balance, Restricted Shares of Common Stock 964,820 598,815
Granted, Restricted Shares of Common Stock 586,648 529,100
Vested, Restricted Shares of Common Stock (235,774) (149,709)
Forfeited, Restricted Shares of Common Stock (18,110) (13,386)
Ending Balance, Restricted Shares of Common Stock 1,297,584 964,820
Beginning Balance, Weighted Average Share Price $ 13.41 $ 12.50
Granted, Weighted Average Share Price 17.29 14.18
Vested, Weighted Average Share Price 13.16 12.50
Forfeited, Weighted Average Share Price 15.54 12.99
Ending Balance, Weighted Average Share Price $ 15.18 $ 13.41
Beginning Balance, Fair Value of Restricted Shares of Common Stock $ 12.9 $ 7.5
Granted, Fair Value of Restricted Shares of Common Stock 10.2 7.5
Vested, Fair Value of Restricted Shares of Common Stock (3.1) (1.9)
Forfeited, Fair Value of Restricted Shares of Common Stock (0.3) (0.2)
Ending Balance, Fair Value of Restricted Shares of Common Stock $ 19.7 $ 12.9