Shareholders Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			3 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		0 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Quarterly [Member]	Dec. 31, 2012 Long Term Capital Gain [Member] Special [Member]	Jan. 17, 2013 Subsequent Event [Member] Quarterly [Member]	Dec. 31, 2013 Subsequent Event [Member] Quarterly [Member]	Dec. 31, 2012 Series A Preferred Stock [Member] Convertible Preferred Stock [Member]	Dec. 31, 2011 Series A Preferred Stock [Member] Convertible Preferred Stock [Member]	Aug. 16, 2012 Series E Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series E Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series E Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series F Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series F Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series G Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series G Preferred Stock [Member] Redeemable Preferred Stock [Member]	Feb. 19, 2013 Series H Preferred Stock [Member] Subsequent Event [Member]	Dec. 31, 2012 Series H Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series H Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series I Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series I Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series J Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series J Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series K Preferred Stock [Member] Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series K Preferred Stock [Member] Redeemable Preferred Stock [Member]	Jul. 11, 2012 Series K Preferred Stock [Member] Public Offering [Member] Redeemable Preferred Stock [Member]
Class Of Stock [Line Items]
Accumulated other comprehensive (loss) income	$ (18,946)	$ 73,729
Common Stock Number Of Shares Par Value And Other Disclosures Abstract
Common shares of beneficial interest: outstanding shares	186,734,711	185,080,020
Dividends Common Stock	699,318	508,745	474,299
DIVIDENDS PER COMMON SHARE				$ 0.69	$ 1.00	$ 0.73	$ 2.92
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock Dividend Rate Percentage								6.50%		7.00%	7.00%		6.75%		6.625%		6.75%	6.75%		6.625%		6.875%		5.70%		5.70%
Preferred shares of beneficial interest: authorized shares	110,000,000	110,000,000						83,977	83,977		3,000,000	3,000,000	6,000,000	6,000,000	8,000,000	8,000,000		4,500,000	4,500,000	10,800,000	10,800,000	9,850,000	9,850,000	12,000,000	0
Preferred Stock, Value	1,240,278	1,021,660						1,682	1,787		0	72,248	144,720	144,720	193,135	193,135		108,549	108,549	262,379	262,379	238,842	238,842	290,971	0
Preferred shares of beneficial interest: outstanding shares	51,184,609	42,186,709						34,609	36,709		0	3,000,000	6,000,000	6,000,000	8,000,000	8,000,000		4,500,000	4,500,000	10,800,000	10,800,000	9,850,000	9,850,000	12,000,000	0
Preferred Stock Liquidation Preference (in dollars per share)								$ 50.00			$ 25.00		$ 25.00		$ 25.00			$ 25.00		$ 25.00		$ 25.00		$ 25.00
Preferred Stock, Dividend Rate, Per-Dollar-Amount								$ 3.25			$ 1.75		$ 1.6875		$ 1.656			$ 1.6875		$ 1.656		$ 1.71875		$ 1.425
Preferred Stock, Additional Disclosure [Abstract]
Preferred shares of beneficial interest: issued shares	51,184,609	42,186,709																								12,000,000
Preferred Stock, Par or Stated Value Per Share																										$ 25.00
Proceeds from the issuance of shares, Value	290,971	238,842
Stock Redeemed Or Called During Period Value	72,248		35,600
Preferred Stock Redemption Price Per Share											$ 25.00				$ 25.00					$ 25.00		$ 25.00		$ 25.00		$ 25.00
Preferred Stock Redemption Discount	8,948	5,000	4,382
Conversion Rate of Preferred Stock to Common Stock, Shares								1.4334
Proceeds from the issuance of preferred shares	290,971	238,842	0																							290,971
Preferred Stock, Redemption Amount										$ 75,000
Preferred Stock Issued Additional Disclosure																										We retained aggregate net proceeds of $290,971,000, after underwriters’ discounts and issuance costs and contributed the net proceeds to the Operating Partnership in exchange for 12,000,000 Series K Preferred Units (with economic terms that mirror those of the Series K Preferred Shares).