Annual report pursuant to Section 13 and 15(d)

Summary of Restricted Stock Activity (Detail)

v3.8.0.1
Summary of Restricted Stock Activity (Detail) - Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Shares of Restricted Stock      
Shares of Restricted Stock, Beginning balance 606,618 757,775 878,897
Shares of Restricted Stock, Granted 246,534 335,707 226,212
Shares of Restricted Stock, Vested (192,230) (430,056) (329,437)
Shares of Restricted Stock, Forfeited (10,341) (56,808) (17,897)
Shares of Restricted Stock, Ending balance 650,581 606,618 757,775
Weighted Average Grant Date Fair Value      
Weighted Average Grant Date Fair Value Outstanding, Beginning $ 33.51 $ 30.73 $ 24.92
Weighted Average Grant Date Fair Value, Granted 41.70 30.98 42.79
Weighted Average Grant Date Fair Value, Vested 36.26 26.60 23.72
Weighted Average Grant Date Fair Value, Forfeited 33.48 33.81 27.58
Weighted Average Grant Date Fair Value Outstanding, Ending $ 35.81 $ 33.51 $ 30.73