Consolidated Statements Of Equity - USD ($) $ in Thousands	Total	Common Shares Of Beneficial Interest	Additional Paid-In Capital	Distributions In Excess Of Net Income	Treasury Shares, At Cost	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Equity, Beginning Balance at Dec. 31, 2015	$ 2,892,896	$ 976	$ 3,662,864	$ (458,577)	$ (386,793)	$ (1,913)	$ 76,339
Net Income	838,226			819,823			18,403
Other comprehensive income	50					50
Proceeds from issuance of common shares	0
Net share awards	24,996		15,213		9,783
Employee share purchase plan	1,697		944		753
Common share options exercised	3,921		1,003		2,918
Change in classification of deferred compensation plan	(13,956)		(13,956)
Change in redemption value of non-qualified share awards	(9,145)			(9,145)
Diversification of share awards within deferred compensation plan	25,428		11,931	13,497
Conversions and redemptions of operating partnership units	(80)		290				(370)
Cash distributions declared to equity holders	(668,470)			(654,778)			(13,692)
Other	(10)	2	(12)
Equity, Ending Balance at Dec. 31, 2016	3,095,553	978	3,678,277	(289,180)	(373,339)	(1,863)	80,680
Net Income	200,860			196,422			4,438
Other comprehensive income	1,806					1,806
Proceeds from issuance of common shares	445,038
Common shares issued		48	444,990
Net share awards	23,956		15,779		8,177
Employee share purchase plan	1,716		1,030		686
Common share options exercised	931		521		410
Change in classification of deferred compensation plan	(13,388)		(13,388)
Change in redemption value of non-qualified share awards	(10,038)			(10,038)
Diversification of share awards within deferred compensation plan	23,233		10,159	13,074
Conversions and redemptions of operating partnership units	0		117				(117)
Cash distributions declared to equity holders	(284,631)			(278,981)			(5,650)
Other	(322)	2	(324)
Equity, Ending Balance at Dec. 31, 2017	3,484,714	1,028	4,137,161	(368,703)	(364,066)	(57)	79,351
Net Income	160,694			156,128			4,566
Other comprehensive income	6,986					6,986
Proceeds from issuance of common shares	0
Net share awards	21,681		13,720		7,961
Employee share purchase plan	1,380		826		554
Common share options exercised	41		41		0
Change in classification of deferred compensation plan	(16,407)		(16,407)
Change in redemption value of non-qualified share awards	669			669
Diversification of share awards within deferred compensation plan	40,294		29,379	10,915
Treasury Stock, Value, Acquired, Par Value Method	(253)				(253)
Conversions and redemptions of operating partnership units	(14,415)		(9,781)				(4,634)
Cash distributions declared to equity holders	(300,107)			(294,505)			(5,602)
Other	(173)	3	(176)
Equity, Ending Balance at Dec. 31, 2018	$ 3,385,104	$ 1,031	$ 4,154,763	$ (495,496)	$ (355,804)	$ 6,929	$ 73,681