CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Total Stockholders' Equity	Shares	Additional Paid-in Capital	Accumulated Deficit	Noncontrolling Interests
Balance at Dec. 31, 2011	$ 3,164,651	$ 2,813,337	$ 1,321	$ 3,490,647	$ (678,631)	$ 351,314
Balance (in shares) at Dec. 31, 2011			132,153,444
Increase (Decrease) in Stockholders' Equity
Net income	366,389	337,426			337,426	28,963
Amortization of share and unit-based plans	14,970	14,970	6	14,964
Amortization of share and unit-based plans (in shares)			566,717
Exercise of stock options	307	307		307
Exercise of stock options (in shares)			10,800
Exercise of stock warrants	(7,371)	(7,371)		(7,371)
Employee stock purchases	956	956		956
Employee stock purchases (in shares)			20,372
Stock offerings, net	175,649	175,649	30	175,619
Stock offerings, net (in shares)	2,961,903		2,961,903
Stock issued to acquire properties	30,000	30,000	5	29,995
Stock issued to acquire property (in shares)			535,265
Distributions paid	(298,536)	(298,536)			(298,536)
Distributions to noncontrolling interests	(30,694)					(30,694)
Contributions from noncontrolling interests	605					605
Other	(589)	(589)		(589)
Conversion of noncontrolling interests to common shares		26,991	13	26,978		(26,991)
Conversion of noncontrolling interests to common shares (in shares)			1,258,509
Redemption of noncontrolling interests	(86)	(58)		(58)		(28)
Adjustment of noncontrolling interests in Operating Partnership		(15,553)		(15,553)		15,553
Balance at Dec. 31, 2012	3,416,251	3,077,529	1,375	3,715,895	(639,741)	338,722
Balance (in shares) at Dec. 31, 2012			137,507,010
Increase (Decrease) in Stockholders' Equity
Net income	448,959	420,090			420,090	28,869
Amortization of share and unit-based plans	28,122	28,122	0	28,122
Amortization of share and unit-based plans (in shares)			88,039
Exercise of stock options	99	99		99
Exercise of stock options (in shares)			2,700
Employee stock purchases	1,089	1,089		1,089
Employee stock purchases (in shares)			22,112
Stock offerings, net	171,102	171,102	25	171,077
Stock offerings, net (in shares)	2,456,956		2,456,956
Distributions paid	(329,155)	(329,155)			(329,155)
Distributions to noncontrolling interests	(31,202)					(31,202)
Contributions from noncontrolling interests	18,079					18,079
Other	(3,561)	(3,561)		(3,561)
Conversion of noncontrolling interests to common shares		12,984	7	12,977		(12,984)
Conversion of noncontrolling interests to common shares (in shares)			656,866
Redemption of noncontrolling interests	(1,066)	(733)		(733)		(333)
Adjustment of noncontrolling interests in Operating Partnership		(18,817)		(18,817)		18,817
Balance at Dec. 31, 2013	3,718,717	3,358,749	1,407	3,906,148	(548,806)	359,968
Balance (in shares) at Dec. 31, 2013	140,733,683		140,733,683
Increase (Decrease) in Stockholders' Equity
Net income	1,606,931	1,499,042			1,499,042	107,889
Amortization of share and unit-based plans	34,873	34,873	2	34,871
Amortization of share and unit-based plans (in shares)			168,379
Employee stock purchases	1,231	1,231		1,231
Employee stock purchases (in shares)			25,007
Stock issued to acquire properties	1,161,274	1,161,274	172	1,161,102
Stock issued to acquire property (in shares)			17,140,845
Distributions paid	(353,495)	(353,495)			(353,495)
Distributions to noncontrolling interests	(32,230)					(32,230)
Other	(97,216)	(3,858)		(3,858)		(93,358)
Conversion of noncontrolling interests to common shares		2,410	1	2,409		(2,410)
Conversion of noncontrolling interests to common shares (in shares)			134,082
Redemption of noncontrolling interests	(236)	(157)		(157)		(79)
Adjustment of noncontrolling interests in Operating Partnership		(59,949)		(59,949)		59,949
Balance at Dec. 31, 2014	$ 6,039,849	$ 5,640,120	$ 1,582	$ 5,041,797	$ 596,741	$ 399,729
Balance (in shares) at Dec. 31, 2014	158,201,996		158,201,996