Summary of Restricted Stock Activity (Detail) (Restricted Stock, USD $)	9 Months Ended
	Sep. 30, 2014
Restricted Stock
Shares of Restricted Stock
Shares of Restricted Stock, Beginning balance	1,260,913
Shares of Restricted Stock, Granted	268,257
Shares of Restricted Stock, Vested	(619,307)
Shares of Restricted Stock, Forfeited	(17,388)
Shares of Restricted Stock, Ending balance	892,475
Shares of Restricted Stock, Unvested restricted stock	892,475
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value Outstanding, Beginning	$ 21.85
Weighted Average Grant Date Fair Value, Granted	$ 28.90
Weighted Average Grant Date Fair Value, Vested	$ 20.50
Weighted Average Grant Date Fair Value, Forfeited	$ 21.42
Weighted Average Grant Date Fair Value Outstanding, Ending	$ 24.91
Weighted Average Grant Date Fair Value, Unvested restricted stock	$ 24.91