Subsequent Events (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended
	Mar. 31, 2015 property	Dec. 31, 2014	May 04, 2015 property	May 08, 2015
Subsequent Event [Line Items]
Number of acquired centers	2
Gross acquisition purchase price	$ 92,100,000
Number of operating properties sold	3
Proceeds from sale and disposition of property	34,600,000
6.5% Series F Preferred Shares [Member]
Subsequent Event [Line Items]
Preferred shares dividend percentage	6.50%	6.50%
Subsequent Event [Member]
Subsequent Event [Line Items]
Number of acquired centers			1
Gross acquisition purchase price			53,500,000
Number of operating properties sold			2
Proceeds from sale and disposition of property			9,300,000
Subsequent Event [Member] | Interest Rate Contracts [Member]
Subsequent Event [Line Items]
Number of forward interest rate contracts			2
Derivative, notional amount			215,000,000
Subsequent Event [Member] | Interest Rate Swap [Member]
Subsequent Event [Line Items]
Derivative, Remaining Maturity			10 years
Derivative, fixed Interest rate			2.00%
Scenario, Forecast [Member] | 6.5% Series F Preferred Shares [Member]
Subsequent Event [Line Items]
Preferred shares settled				150,000,000
Redemption costs of preferred shares				$ 9,800,000