Income Taxes - Income Tax Characterization of Dividends (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Income Tax Characterization Of Dividends Paid [Line Items]
Ordinary income, Amount	$ 0.53	$ 0.23
Capital gains	$ 0.07
Unrecaptured Section 1250 gains	$ 0.06
Return of capital	$ 0.28	$ 0.59	$ 0.80
Dividends paid per common share	$ 0.94	$ 0.82	$ 0.80
Percentage of Ordinary income	56.60%	28.00%
Percentage of Capital gains	7.00%
Percentage of Unrecaptured Section 1250 gains	6.90%
Percentage of Return of capital	29.50%	72.00%	100.00%
Percentage of dividend paid per common share	100.00%	100.00%	100.00%