Shareholders' Equity Shareholders' Equity Summary of Dividends (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Common Shares [Member]
Dividends [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.730	$ 0.690
Common Stock, Dividends, Per Share, Cash Paid	$ 0.730	$ 0.690
5.417% Series 1 Cumulative Convertible Preferred [Member]
Dividends [Line Items]
Preferred Stock, Dividend Rate, Percentage	5.417%	5.417%	5.417%
Preferred Stock, Dividends Per Share, Declared	$ 0.339	$ 0.339
Preferred Stock, Dividends, Per Share, Cash Paid	$ 0.339	$ 0.339