Annual report pursuant to Section 13 and 15(d)

Summary of Restricted Stock Activity (Detail)

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Summary of Restricted Stock Activity (Detail) (Restricted Stock, USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Restricted Stock
     
Shares of Restricted Stock      
Shares of Restricted Stock, Beginning balance 1,534,163 1,384,390 1,254,691
Shares of Restricted Stock, Granted 271,532 653,229 424,436
Shares of Restricted Stock, Vested (522,129) (489,033) (288,204)
Shares of Restricted Stock, Canceled     (4,613)
Shares of Restricted Stock, Forfeited (22,653) (14,423) (1,920)
Shares of Restricted Stock, Ending balance 1,260,913 1,534,163 1,384,390
Weighted Average Grant Date Fair Value      
Weighted Average Grant Date Fair Value Outstanding, Beginning $ 18.85 $ 16.85 $ 14.60
Weighted Average Grant Date Fair Value, Granted $ 30.09 $ 21.70 $ 19.45
Weighted Average Grant Date Fair Value, Vested $ 17.27 $ 17.00 $ 10.84
Weighted Average Grant Date Fair Value, Canceled     $ 18.35
Weighted Average Grant Date Fair Value, Forfeited $ 22.92 $ 18.58 $ 14.34
Weighted Average Grant Date Fair Value Outstanding, Ending $ 21.86 $ 18.85 $ 16.85