Capital Stock (Details 3)	12 Months Ended
	Dec. 31, 2012
Excess Share Provision
Percentage of beneficial ownership of common stock acquired used as threshold for determining excess shares	9.00%
Percentage of beneficial ownership of preferred stock acquired used as threshold for determining excess shares	9.90%
Maximum deferral payment period of purchase price for excess shares (in years)	5 years
Distribution Reinvestment and Stock Purchase Plan
Discount on purchase price of common stock to shareholders reinvesting their dividends and/or make optional cash purchases through the DRIP (as a percent)	1.00%