Quarterly Financial Data (Unaudited) (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Selected Quarterly Financial Information [Line Items]
Revenues	$ 142,863	$ 138,599	$ 135,676	$ 132,417	$ 129,654	$ 130,787	$ 126,804	$ 125,599	$ 549,555	$ 512,844	$ 514,406
Net income	69,176	61,337	37,651	108,667	49,026	45,188	37,786	49,222	276,831	181,222	307,579
Net income attributable to common shareholders	$ 44,142	$ 51,901	$ 35,816	$ 107,074	$ 47,275	$ 43,401	$ 25,222	$ 44,937	$ 238,933	$ 160,835	$ 277,168
Earnings per common share - basic (in dollars per share)	$ 0.35	$ 0.41	$ 0.28	$ 0.87	$ 0.38	$ 0.35	$ 0.20	$ 0.37	$ 1.90	$ 1.31	$ 2.28
Earnings per common share - diluted (in dollars per share)	$ 0.34	$ 0.40	$ 0.28	$ 0.85	$ 0.38	$ 0.35	$ 0.20	$ 0.36	$ 1.87	$ 1.29	$ 2.25
Gain on sale of properties and real estate joint venture and partnership interests and on acquisitions	$ 34,900	$ 31,100	$ 4,200	$ 82,800	$ 15,700	$ 13,200	$ 8,200	$ 23,400
Gain on sale of property		1,100		$ 5,900					$ 100,714	$ 59,621	$ 190,872
Debt extinguishment costs			$ (2,000)					$ 6,100
Redemption costs of preferred shares									0	9,687	0
Net income attributable to noncontrolling interests	$ 23,100	$ 5,800							37,898	$ 6,870	$ 19,571
6.5% Series F Preferred Shares [Member]
Schedule of Selected Quarterly Financial Information [Line Items]
Redemption costs of preferred shares							$ 9,700
Fair Value Hedging [Member] | Interest Rate Contracts [Member]
Schedule of Selected Quarterly Financial Information [Line Items]
Proceeds from extinguishment of derivative instrument									$ 2,200