Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Dividends In Excess Of Earnings [Member]	Treasury Stock, At Cost [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]
Equity, value at Dec. 31, 2012	$ 5,634,854	$ 1,516		$ 5,222,073	$ (109,985)	$ (2,722)	$ (13,817)	$ 537,789
Equity, shares at Dec. 31, 2012		151,601,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		9,000
Conversion of operating partnership units to Common Stock, value	0	0		272				(272)
Allocated net income for the year	54,743				48,000			6,743
Dividends/distributions declared	(110,158)				(98,712)			(11,446)
Issuance of 5.25% Series B cumulative redeemable preferred stock	194,371		200,000	(5,629)
Sale of common stock, net of offering costs		0
Sale of common stock, net of offering costs		0
Shares issued pursuant to stock purchase plan, shares		3,000
Shares issued pursuant to stock purchase plan, value	335			335
Net activity from stock option and incentive plan, shares		27,000
Net activity from stock option and incentive plan, value	20,806	0		4,262				16,544
Contributions from noncontrolling interests in property partnerships	10,421							10,421
Distributions to noncontrolling interests in property partnerships	(750)							(750)
Amortization of interest rate contracts	628						564	64
Reallocation of noncontrolling interest	0			10,717				(10,717)
Equity, value at Mar. 31, 2013	5,805,250	1,516	200,000	5,232,030	(160,697)	(2,722)	(13,253)	548,376
Equity, shares at Mar. 31, 2013		151,640,000
Equity, value at Dec. 31, 2013	7,043,618	1,530	200,000	5,662,453	(108,552)	(2,722)	(11,556)	1,302,465
Equity, shares at Dec. 31, 2013	152,983,101	152,983,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of operating partnership units to Common Stock, shares		18,000
Conversion of operating partnership units to Common Stock, value				627				(627)
Allocated net income for the year	65,369				56,623			8,746
Dividends/distributions declared	(113,268)				(102,050)			(11,218)
Shares issued pursuant to stock purchase plan, shares		4,000
Shares issued pursuant to stock purchase plan, value	357			357
Net activity from stock option and incentive plan, shares		12,000
Net activity from stock option and incentive plan, value	9,464			704				8,760
Contributions from noncontrolling interests in property partnerships	468							468
Distributions to noncontrolling interests in property partnerships	(4,093)							(4,093)
Amortization of interest rate contracts	629						567	62
Reallocation of noncontrolling interest				4,089				(4,089)
Equity, value at Mar. 31, 2014	$ 7,002,544	$ 1,530	$ 200,000	$ 5,668,230	$ (153,979)	$ (2,722)	$ (10,989)	$ 1,300,474
Equity, shares at Mar. 31, 2014	153,017,311	153,017,000