Equity Offerings (Details) (USD $) Share data in Millions, unless otherwise specified	9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Common Shares Equity Offering [Member] Common Stock [Member]	Sep. 30, 2013 Continuous Equity Offering [Member] Common Stock [Member]	Sep. 30, 2013 Continuous Equity Offering [Member] Common Stock [Member]
Class of Stock [Line Items]
Common stock, Continuous equity offering program, Max amount of equity				$ 200,000,000	$ 200,000,000
Stock Issued During Period, Shares, New Issues			24.2	0	1.9
Net proceeds from issuance of common shares	$ 954,481,000	$ 42,808,000	$ 834,100,000		$ 75,000,000