Quarterly Financial Data (Unaudited) (Schedule Of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 139,367	$ 144,110	$ 146,023	$ 143,663	$ 142,863	$ 138,599	$ 135,676	$ 132,417	$ 573,163	$ 549,555	$ 512,844
Net Income	170,653	74,473	69,193	36,396	69,176	61,337	37,651	108,667	350,715	276,831	181,222
Net income attributable to common shareholders	$ 167,967	$ 72,629	$ 63,852	$ 30,826	$ 44,142	$ 51,901	$ 35,816	$ 107,074	$ 335,274	$ 238,933	$ 160,835
Net income attributable to common shareholders - basic (in dollars per share)	$ 1.31	$ 0.57	$ 0.50	$ 0.24	$ 0.35	$ 0.41	$ 0.28	$ 0.87	$ 2.62	$ 1.90	$ 1.31
Net income attributable to common shareholders - diluted (in dollars per share)	$ 1.30	$ 0.56	$ 0.49	$ 0.24	$ 0.34	$ 0.40	$ 0.28	$ 0.85	$ 2.60	$ 1.87	$ 1.29
Gain on sale of properties and real estate joint venture and partnership interests and on acquisitions	$ 136,300	$ 38,600	$ 34,200	$ 15,800	$ 34,900	$ 31,100	$ 4,200	$ 82,800
Impairment losses related to property				3,100
Impairment loss				15,000					$ 15,257	$ 98	$ 153
Net income attributable to noncontrolling interests			$ 3,600	3,900	$ 23,100	5,800			15,441	37,898	6,870
Gain on sale of property	$ 1,500			$ (3,300)		$ 1,100		$ 5,900	$ 218,611	$ 100,714	$ 59,621
Gain (loss) on debt extinguishment							$ 2,000