Shareholders Equity (Narrative) (Details) (USD $)	12 Months Ended						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 At The Market Equity Program [Member]	Dec. 31, 2012 At The Market Equity Program [Member]	May 08, 2012 At The Market Equity Program [Member]	Dec. 31, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Dec. 31, 2013 5.417% Series 1 Cumulative Convertible Preferred [Member]	Dec. 31, 2012 5.417% Series 1 Cumulative Convertible Preferred [Member]	Dec. 31, 2011 5.417% Series 1 Cumulative Convertible Preferred [Member]	Dec. 31, 2013 Commissions [Member] At The Market Equity Program [Member]	Dec. 31, 2012 Commissions [Member] At The Market Equity Program [Member]	Dec. 31, 2013 Other Offering Costs [Member] At The Market Equity Program [Member]	Dec. 31, 2012 Other Offering Costs [Member] At The Market Equity Program [Member]
Shares issued under dividend reinvestment plan (in shares)	20,026	22,814	28,823				20,026	22,814	28,823
Preferred shares, shares outstanding	399,896	399,896	399,896
Preferred Shares, percentage										5.417%	5.417%	5.417%
Preferred Stock, Liquidation Preference Per Share	$ 25	$ 25	$ 25
Common Stock, Shares, Issued	66,701,422	64,815,446
Preferred shares, par	$ 0.01	$ 0.01	$ 0.01
Convertible Preferred Stock, Converstion Price Per Share	$ 104.69
Aggregate offering price of common share						$ 300,000,000
Shares issued under equity program				1,734,974	1,040,946		1,735,089	1,039,405	1,662,230
Weighted average price per common share				$ 108.01	$ 103.69
Net cash proceeds of common stock	186,548,000	112,270,000	154,921,000	185,200,000	106,400,000
Commissions related to sales of common shares													2,000,000	1,400,000	200,000	200,000
Remaining Capacity To Issue	$ 26,000,000