Preferred Shares (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015
Series H and I Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable preferred stock redemption price per share	$ 25.00
Preferred stock redeemable term (in days)	120 days
7 1/2% Series H Preferred Shares [Member]
Class of Stock [Line Items]
Cumulative Redeemable Preferred Shares, Stated Percentage	7.50%
Shares issued upon conversion	4,680,500
6 3/8% Series I Preferred Stock [Member]
Class of Stock [Line Items]
Cumulative Redeemable Preferred Shares, Stated Percentage	6.375%
Shares issued upon conversion	8,835,200