Subsequent Events (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 Integer	Mar. 31, 2011	Dec. 31, 2011
Subsequent Event [Line Items]
Date Dividends Declared	2012-04
Date Dividends Will Be Paid	2012-05
Common Stock, Dividends Per Share, Declared (dollars per share)	$ 0.1458125
Preferred Stock Class E, Dividends Per Share, Declared (dollars per share)	$ 0.140625
Preferred Stock Class F Dividends Per Share Declared	$ 0.138021
Preferred stock, shares issued (in shares)	23,750,000		13,900,000
Underwriting discounts and other offering costs	$ 12,800,000
Proceeds from preferred stock offering, net	360,941,000	0
Anticipated acquired properties	514,000,000
Number Of New Real Estate Properties, Subsequent Events	250
Number of tenants property is leased to	4
Issuance of Cumulative Redeemable Preferred Stock Class F [Member]
Subsequent Event [Line Items]
Preferred stock, shares issued (in shares)	1,400,000
Preferred stock, redemption price per share (in dollars per share)	$ 25.2863
Underwriting discounts and other offering costs	1,000,000
Proceeds from preferred stock offering, net	$ 34,400,000