Summary of Restricted Stock Activity (Detail) (Restricted Stock, USD $)	6 Months Ended
	Jun. 30, 2014
Restricted Stock
Shares of Restricted Stock
Shares of Restricted Stock, Beginning balance	1,260,913
Shares of Restricted Stock, Granted	261,213
Shares of Restricted Stock, Vested	(619,307)
Shares of Restricted Stock, Forfeited	(12,186)
Shares of Restricted Stock, Ending balance	890,633
Shares of Restricted Stock, Unvested restricted stock	890,633
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value Outstanding, Beginning	$ 21.85
Weighted Average Grant Date Fair Value, Granted	$ 28.72
Weighted Average Grant Date Fair Value, Vested	$ 20.50
Weighted Average Grant Date Fair Value, Forfeited	$ 19.61
Weighted Average Grant Date Fair Value Outstanding, Ending	$ 24.83
Weighted Average Grant Date Fair Value, Unvested restricted stock	$ 24.83