Consolidated Statement of Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In-Capital	Treasury Stock	Accumulated Other Comprehensive Income	Retained Earnings	Noncontrolling Interests	Series I Preferred Stock Preferred Stock
Beginning Balance at Dec. 31, 2016	$ 7,750,911	$ 221,932	$ 1,017	$ 5,624,545	$ (124,049)	$ 22,137	$ 1,578,893	$ 426,436
Beginning Balance (in shares) at Dec. 31, 2016			100,562
Increase (Decrease) in Stockholders' Equity
Net income	10,343						27,048	(16,705)
Other comprehensive income	(7,783)					(7,783)
Preferred dividends	(7,475)						(7,475)
DRSPP proceeds (in shares)			1
DRSPP proceeds	111			111
Conversion of units of the Operating Partnership to common stock (in shares)			122
Conversion of units in the Operating Partnership for common stock	13,242		$ 1	13,241
Reallocation of noncontrolling interest in the Operating Partnership	(12,712)						(12,712)
Equity component of repurchased exchangeable senior notes	(18,824)			(18,824)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)			(8)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	13,544			13,544
Repurchases of common stock (in shares)			(2,448)
Repurchases of common stock	(253,197)		$ (24)	(253,173)
Proceeds from stock options exercised (in shares)			138
Proceeds from stock options exercised	11,595		$ 1	11,594
Contributions to consolidated joint venture interests	33,009							33,009
Deconsolidation of partially owned entity	(30,203)							(30,203)
Cash distributions to noncontrolling interests	(609)							(609)
Cash distributions declared (per common share, none of which represented a return of capital for federal income tax purposes)	(154,312)						(154,312)
Ending Balance at Jun. 30, 2017	7,347,640	221,932	$ 995	5,391,038	(124,049)	14,354	1,431,442	411,928
Ending Balance (in shares) at Jun. 30, 2017			98,367
Beginning Balance at Dec. 31, 2016	7,750,911	221,932	$ 1,017	5,624,545	(124,049)	22,137	1,578,893	426,436
Beginning Balance (in shares) at Dec. 31, 2016			100,562
Increase (Decrease) in Stockholders' Equity
Preferred dividends	(11,213)
Ending Balance at Sep. 30, 2017	7,184,052	221,932	$ 985	5,294,500	(124,049)	14,185	1,410,332	366,167
Ending Balance (in shares) at Sep. 30, 2017			97,446
Beginning Balance at Jun. 30, 2017	7,347,640	221,932	$ 995	5,391,038	(124,049)	14,354	1,431,442	411,928
Beginning Balance (in shares) at Jun. 30, 2017			98,367
Increase (Decrease) in Stockholders' Equity
Net income	41,133						42,607	(1,474)
Other comprehensive income	(169)					(169)
Preferred dividends	(3,738)						(3,738)
DRSPP proceeds (in shares)			1
DRSPP proceeds	74			74
Conversion of units of the Operating Partnership to common stock (in shares)			20
Conversion of units in the Operating Partnership for common stock	2,111		$ 0	2,111
Reallocation of noncontrolling interest in the Operating Partnership	15,381						15,381
Equity component of repurchased exchangeable senior notes	(9,145)			(9,145)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)			2
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	6,511			6,511
Repurchases of common stock (in shares)			(952)
Repurchases of common stock	(96,794)		$ (10)	(96,784)
Proceeds from stock options exercised (in shares)			8
Proceeds from stock options exercised	695		$ 0	695
Contributions to consolidated joint venture interests	193							193
Deconsolidation of partially owned entity	0							0
Cash distributions to noncontrolling interests	(44,480)							(44,480)
Cash distributions declared (per common share, none of which represented a return of capital for federal income tax purposes)	(75,360)						(75,360)
Ending Balance at Sep. 30, 2017	7,184,052	221,932	$ 985	5,294,500	(124,049)	14,185	1,410,332	366,167
Ending Balance (in shares) at Sep. 30, 2017			97,446
Increase (Decrease) in Stockholders' Equity
Cumulative adjustment upon adoption of ASC 610-20 | Accounting Standards Update 2014-09	570,524						570,524
Beginning Balance at Dec. 31, 2017	6,589,454		$ 939	4,968,338	(124,049)	18,604	1,139,329	364,361	$ 221,932
Beginning Balance (in shares) at Dec. 31, 2017			92,803
Adjusted Balance at Dec. 31, 2017	7,159,978		$ 939	4,968,338	(124,049)	18,604	1,709,853	364,361	221,932
Increase (Decrease) in Stockholders' Equity
Net income	213,168						212,797	371
Other comprehensive income	14,018					14,018
Preferred dividends	(7,475)						(7,475)
DRSPP proceeds (in shares)			1
DRSPP proceeds	64			64
Conversion of units of the Operating Partnership to common stock (in shares)			15
Conversion of units in the Operating Partnership for common stock	1,560			1,560
Reallocation of noncontrolling interest in the Operating Partnership	(4,493)						(4,493)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)			(20)
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	8,090			8,090
Repurchases of common stock (in shares)			(7,133)
Repurchases of common stock	(693,091)		$ (72)	(382,080)			(310,939)
Proceeds from stock options exercised (in shares)			59
Proceeds from stock options exercised	5,637		$ 1	5,636
Contributions to consolidated joint venture interests	1,828							1,828
Deconsolidation of partially owned entity	(314,596)							(314,596)
Cash distributions to noncontrolling interests	(724)							(724)
Cash distributions declared (per common share, none of which represented a return of capital for federal income tax purposes)	(141,908)						(141,908)
Ending Balance at Jun. 30, 2018	6,242,056	221,932	$ 868	4,601,608	(124,049)	32,622	1,457,835	51,240
Ending Balance (in shares) at Jun. 30, 2018			85,725
Beginning Balance at Dec. 31, 2017	6,589,454		$ 939	4,968,338	(124,049)	18,604	1,139,329	364,361	221,932
Beginning Balance (in shares) at Dec. 31, 2017			92,803
Adjusted Balance at Dec. 31, 2017	7,159,978		$ 939	4,968,338	(124,049)	18,604	1,709,853	364,361	$ 221,932
Increase (Decrease) in Stockholders' Equity
Preferred dividends	(11,213)
Ending Balance at Sep. 30, 2018	6,267,175	221,932	$ 867	4,602,650	(124,049)	36,299	1,476,959	52,517
Ending Balance (in shares) at Sep. 30, 2018			85,594
Beginning Balance at Jun. 30, 2018	6,242,056	221,932	$ 868	4,601,608	(124,049)	32,622	1,457,835	51,240
Beginning Balance (in shares) at Jun. 30, 2018			85,725
Increase (Decrease) in Stockholders' Equity
Net income	91,811						91,947	(136)
Other comprehensive income	3,677					3,677
Preferred dividends	(3,738)						(3,738)
DRSPP proceeds (in shares)			0
DRSPP proceeds	52			52
Conversion of units of the Operating Partnership to common stock (in shares)			0
Conversion of units in the Operating Partnership for common stock	0
Reallocation of noncontrolling interest in the Operating Partnership	11,941						11,941
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings (in shares)			13
Deferred compensation plan and stock awards, net of forfeitures and tax withholdings	4,634			4,634
Repurchases of common stock (in shares)			(253)
Repurchases of common stock	(25,236)		$ (2)	(13,579)			(11,655)
Proceeds from stock options exercised (in shares)			109
Proceeds from stock options exercised	9,936		$ 1	9,935
Contributions to consolidated joint venture interests	3,072							3,072
Deconsolidation of partially owned entity	(520)							(520)
Cash distributions to noncontrolling interests	(1,139)							(1,139)
Cash distributions declared (per common share, none of which represented a return of capital for federal income tax purposes)	(69,371)						(69,371)
Ending Balance at Sep. 30, 2018	$ 6,267,175	$ 221,932	$ 867	$ 4,602,650	$ (124,049)	$ 36,299	$ 1,476,959	$ 52,517
Ending Balance (in shares) at Sep. 30, 2018			85,594