Earnings Per Share - Schedule Of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
NUMERATOR
Income from continuing operations	$ 54,550	$ 44,648	$ 136,917	$ 130,609
Less: Preferred share dividends	(136)	(136)	(406)	(406)
Less: Net income attributable to noncontrolling interests	(2,103)	(1,974)	(6,161)	(5,637)
Less: Earnings allocated to unvested shares	(221)	(264)	(638)	(739)
Income from continuing operations available for common shareholders	52,090	42,274	129,712	123,827
Gain on sale of real estate	0	4,401	11,509	4,401
Net income available for common shareholders, basic and diluted	$ 52,090	$ 46,675	$ 141,221	$ 128,228
DENOMINATOR
Weighted average common shares outstanding—basic (in shares)	69,006	67,559	68,637	67,095
Stock options (in shares)	175	173	184	166
Weighted average common shares outstanding—diluted (in shares)	69,181	67,732	68,821	67,261
EARNINGS PER COMMON SHARE, BASIC
Continuing operations (in usd per share)	$ 0.75	$ 0.62	$ 1.89	$ 1.84
Gain on sale of real estate (in usd per share)	0.00	0.07	0.17	0.07
Earnings per common share, basic (in usd per share)	0.75	0.69	2.06	1.91
EARNINGS PER COMMON SHARE, DILUTED
Continuing operations (in usd per share)	0.75	0.62	1.88	1.84
Gain on sale of real estate (in usd per share)	0.00	0.07	0.17	0.07
Earnings per common share, diluted (in usd per share)	$ 0.75	$ 0.69	$ 2.05	$ 1.91
Income from continuing operations attributable to the Trust	$ 52,447	$ 42,674	$ 130,756	$ 124,972