Quarterly Financial Data (Unaudited) (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended								12 Months Ended
	May. 08, 2015	Jun. 05, 2013	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Selected Quarterly Financial Information [Line Items]
Revenues			$ 129,654	$ 130,787	$ 126,804	$ 125,599	$ 126,102	$ 130,521	$ 130,191	$ 127,592	$ 512,844	$ 514,406	$ 489,195
Net income			49,026	45,188	37,786	49,222	103,615	102,199	36,984	64,781	181,222	307,579	265,156
Net income attributable to common shareholders			$ 47,275	$ 43,401	$ 25,222	$ 44,937	$ 86,270	$ 97,619	$ 32,686	$ 60,593	$ 160,835	$ 277,168	$ 184,145
Earnings per common share - basic (in dollars per share)			$ 0.38	$ 0.35	$ 0.20	$ 0.37	$ 0.71	$ 0.80	$ 0.27	$ 0.50	$ 1.31	$ 2.28	$ 1.52
Earnings per common share - diluted (in dollars per share)			$ 0.38	$ 0.35	$ 0.20	$ 0.36	$ 0.70	$ 0.79	$ 0.27	$ 0.49	$ 1.29	$ 2.25	$ 1.50
Gain on sale of properties and real estate joint venture and partnership interests and on acquisitions			$ 15,700	$ 13,200	$ 8,200	$ 23,400	$ 74,900	$ 69,500	$ 6,800	$ 41,400
Debt extinguishment costs						$ 6,100
Accelerated depreciation											$ 145,940	$ 150,356	$ 146,763
Tax benefit											$ (52)	$ 1,261	(7,046)
Debt stated interest rate			3.50%				7.40%				3.50%	7.40%
Gain on sale of property											$ 59,621	$ 190,872	119,965
Write-off of debt costs												1,200
Impairment loss											153	1,024	2,579
Net income attributable to noncontrolling interests							$ 14,600				6,870	19,571	44,894
Redemption costs of preferred shares											9,687	0	17,944
6.5% Series F Preferred Shares [Member]
Schedule of Selected Quarterly Financial Information [Line Items]
Preferred stock dividends and other adjustments	$ 9,700				$ 9,700
Redemption costs of preferred shares		$ 15,700
Acceleration Of Mortgage Intangible Amortization [Member]
Schedule of Selected Quarterly Financial Information [Line Items]
Amortization (accretion)													$ (9,700)
Equity Method Investee [Member]
Schedule of Selected Quarterly Financial Information [Line Items]
Gain on sale of property											$ 1,000	$ 4,900
8.1% Senior Unsecured Notes [Member]
Schedule of Selected Quarterly Financial Information [Line Items]
Debt stated interest rate							8.10%					8.10%