Equity Transactions Narrative (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended		1 Months Ended	3 Months Ended	0 Months Ended	9 Months Ended			0 Months Ended	1 Months Ended		9 Months Ended				1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Common Stock	Mar. 31, 2014 Common Stock	Oct. 17, 2014 Common Stock Dividend Paid [Member]	Sep. 30, 2014 Preferred Stock [Member]	Oct. 15, 2014 Preferred Stock [Member] Dividend Paid [Member]	Sep. 30, 2014 Repurchase Agreements [Member] Common Stock	Sep. 30, 2013 Repurchase Agreements [Member] Common Stock	Nov. 30, 2004 Repurchase Agreements [Member] Common Stock	Apr. 08, 2014 Registered public offering [Member] Common Stock	Sep. 30, 2014 Registered public offering [Member] Common Stock	Mar. 31, 2014 Registered public offering [Member] Common Stock	Sep. 30, 2014 Conversion of Common OP Units [Member] Common OP Units [Member]	Sep. 30, 2013 Conversion of Common OP Units [Member] Common OP Units [Member]	Sep. 30, 2014 Series A-1 Preferred OP Units [Member]	Sep. 30, 2014 Series A-1 Preferred OP Units [Member] Common OP Units [Member]	Sep. 30, 2014 Underwriters [Member] Registered public offering [Member] Common Stock
Class of Stock [Line Items]
Authorized to be repurchased (in shares)												1,000,000
Remaining number of shares authorized to be repurchased (in shares)										400,000
Stock Repurchased During Period, Shares										0	0
Conversion of Common OP Units to common stock (in shares)																0	0	18,773	45,785
New shares issued (in shares)													630,000	6,900,000	4,200,000					900,000
Weighted average sale price (in dollars per share)														$ 50.60	$ 44.45
Proceeds from issuance of common stock			$ 562,581,000	$ 261,780,000										$ 348,900,000	$ 214,000,000
Dividends per common share:	$ 0.65	$ 0.63	$ 1.95	$ 1.89	$ 0.65	$ 0.65
Dividends, Common Stock, Cash							32,600,000
Preferred Stock, Dividends Per Share, Declared								$ 0.4453
Dividends, Preferred Stock, Cash									$ 1,500,000