Common Stock and Preferred Stock - Additional Information (Detail) (USD $)	9 Months Ended			9 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Common Stock	Sep. 30, 2012 Cash	Oct. 01, 2012 Scenario, Forecast	May 16, 2012 Common Stock Offering	Sep. 30, 2012 Restricted Stock Year	Sep. 30, 2011 Restricted Stock	Sep. 30, 2012 Dividend and Distribution Reinvestment and Share Purchase Plan
Class of Stock [Line Items]
Common stock, share outstanding	13,769,376	10,944,675	10,954,065
Common stock, share issued							2,760,000			30,490
Common stock price per share							$ 25.25			$ 26.70
Proceed from issuance of common stock							$ 65,700,000			$ 814,200
Restricted stock Vesting Period								4 years
Restricted stock Vesting Percentage Annually								25.00%
Restricted stock available for Awards								677,500
Restricted stock available for Awards								20,000
Restricted stock Issue date								Feb. 03, 2012
Restricted stock Issued								25,600
Restricted Stock Grant date Market Value								720,896
Restricted Stock Non-Vested								53,942	52,362
Restricted Stock Weighted Average Grant Date Fair Value								$ 24.67	$ 22.21
Share Based compensation Expense								1,100,000	500,000
unrecognized share Based compensation								800,000
Share Compensation Recognition period								2.6
Restricted shares forfeited								779
Forfeitures or cancellations under the Stock Plan								0
Restricted stock Issued	0
Fully-vested restricted stock units issued						5,470
Percentage underlying restricted stock that directors will receive				70.00%	30.00%
Dividend Declared	$ 100,000	$ 100,000