Corporate Indebtedness (Details) (USD $)	3 Months Ended				3 Months Ended		1 Months Ended	3 Months Ended								3 Months Ended			0 Months Ended			3 Months Ended		0 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended	12 Months Ended	0 Months Ended	1 Months Ended		3 Months Ended		0 Months Ended	1 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Joint venture	Mar. 31, 2013 2012 Credit Facility	Nov. 30, 2012 2012 Credit Facility	Nov. 30, 2012 Revolving credit facility item	Mar. 31, 2013 Revolving credit facility	Mar. 31, 2013 Revolving credit facility Maximum	Mar. 31, 2013 Revolving credit facility Minimum	Mar. 31, 2013 Term loan	Nov. 30, 2012 Term loan	Mar. 31, 2013 Term loan Maximum	Mar. 31, 2013 Term loan Minimum	Mar. 31, 2013 Term Loan and Senior Unsecured Notes	Mar. 31, 2013 2011 Revolving Credit Facility	Mar. 31, 2013 2011 Revolving Credit Facility Maximum	Mar. 31, 2013 2011 Revolving Credit Facility Minimum	Dec. 27, 2012 Senior Unsecured Notes	Mar. 31, 2013 Senior Unsecured Notes	Dec. 31, 2012 Senior Unsecured Notes	Mar. 31, 2013 5.88% Senior unsecured notes maturing on August 15, 2014	Dec. 31, 2012 5.88% Senior unsecured notes maturing on August 15, 2014	Dec. 27, 2012 6.00% Senior unsecured notes maturing on March 31, 2016	Mar. 31, 2013 6.00% Senior unsecured notes maturing on March 31, 2016	Dec. 31, 2012 6.00% Senior unsecured notes maturing on March 31, 2016	Oct. 31, 2010 3.00% Senior unsecured notes maturing on October 15, 2017	Mar. 31, 2013 3.00% Senior unsecured notes maturing on October 15, 2017	Dec. 31, 2012 3.00% Senior unsecured notes maturing on October 15, 2017	Mar. 31, 2013 5.00% senior unsecured notes maturing on August 15, 2018	Dec. 31, 2012 5.00% senior unsecured notes maturing on August 15, 2018	Mar. 31, 2013 7.75% Senior unsecured notes maturing on March 15, 2020	Dec. 31, 2012 7.75% Senior unsecured notes maturing on March 15, 2020	Mar. 31, 2013 4.50% senior unsecured notes maturing on December 1, 2022	Dec. 31, 2012 4.50% senior unsecured notes maturing on December 1, 2022	Mar. 31, 2013 4.00% Senior unsecured notes maturing on June 15, 2025	Dec. 31, 2012 4.00% Senior unsecured notes maturing on June 15, 2025	Jan. 02, 2013 3.00% Senior unsecured notes maturing on March 30, 2027	Mar. 31, 2012 3.00% Senior unsecured notes maturing on March 30, 2027	Mar. 31, 2007 3.00% Senior unsecured notes maturing on March 30, 2027	Mar. 31, 2013 3.00% Senior unsecured notes maturing on March 30, 2027	Dec. 31, 2012 3.00% Senior unsecured notes maturing on March 30, 2027	Dec. 27, 2012 5.875% Senior unsecured notes	Jun. 30, 2005 Term Loans and Trust Preferred Securities	Mar. 31, 2013 Term Loans and Trust Preferred Securities	Mar. 31, 2013 Mortgages and other loans payable
Corporate Indebtedness
Revolving credit facility, maximum borrowing capacity						$ 1,600,000,000	$ 1,200,000,000					$ 400,000,000				$ 1,500,000,000
Number of extension options							2
Interest rate, description					LIBOR											LIBOR
Interest rate added to base rate (as a percent)								1.45%	1.75%	1.00%	1.65%		2.00%	1.15%			1.85%	1.00%
Extension option available							6 months
Extension fee required to be paid (as a percent)							0.10%
Maximum borrowing capacity, optional expansion							1,500,000,000
Facility fee on total commitments, payable quarterly in arrears (as a percent)								0.30%	0.35%	0.15%							0.45%	0.175%
Ability to borrow under line of credit facility					1,200,000,000
Outstanding under line of credit facility	30,000,000		70,000,000					30,000,000			400,000,000
Debt disclosures by scheduled maturity date
Unpaid Principal Balance																				1,388,166,000		75,898,000			255,308,000			345,000,000		250,000,000		250,000,000		200,000,000		7,000					11,953,000
Accreted Balance	1,732,588,000		1,734,956,000																	1,332,588,000	1,334,956,000	75,898,000	75,898,000		255,175,000	255,165,000		289,919,000	287,373,000	249,636,000	249,620,000	250,000,000	250,000,000	200,000,000	200,000,000	7,000	7,000				11,953,000	16,893,000
Coupon Rate (as a percent)																						5.88%		6.00%	6.00%			3.00%		5.00%		7.75%		4.50%		4.00%					3.00%		5.875%		5.61%
Effective Rate (as a percent)																						5.88%			6.02%			7.13%		5.03%		7.75%		4.50%		4.00%					3.00%
Term (in years)																						10 years			10 years			7 years		7 years		10 years		10 years		20 years					20 years
Aggregate principal amount of notes repurchased																			42,400,000					19,700,000														4,900,000					22,700,000
Amount of convertible debt recorded in equity																											78,300,000	55,100,000												66,600,000
Loss on early extinguishment of debt	18,513,000																		3,800,000
Debt instrument issued, value																											345,000,000													750,000,000				100,000,000
Premium on sale price to calculate exchange price of notes (as a percent)																											30.00%													25.00%
Exchange price (in dollars per share)																											$ 85.81													$ 173.30
Adjusted exchange rate for the debentures (in shares)																												0.0116800								0.0077461
Repayment of debt																			46,400,000																		650,000		102,200,000
Consideration as a percentage of accrued balance on repayment of debt																																						99.60%
Adjusted reference dividend for debentures																																				1.3491
Maximum consecutive quarters up to which interest payment can be deferred																																													2 years
Number of years for which securities will bear fixed rate of interest																																													10 years
Debt Instrument, Premium Payable on Early Redemption																																													0
Scheduled Amortization
2013																																														30,878,000
2014																																														43,668,000
2015																																														46,325,000
2016																																														56,839,000
2017																																														60,897,000
Thereafter																																														367,307,000
Total amortization of debt																																														605,914,000
Principal Repayments
2013				185,130,000																																										357,308,000
2014				364,191,000																																										146,273,000
2015				36,886,000																																										229,537,000
2016				527,682,000																																										516,667,000
2017				933,612,000																																										1,098,064,000
Thereafter				151,642,000												30,000,000																													100,000,000	1,861,722,000
Total principal repayments				2,199,143,000												30,000,000																													100,000,000	4,209,571,000
Scheduled Amortization and Principal Repayments
2013	388,186,000
2014	265,839,000														75,898,000
2015	275,869,000														7,000
2016	828,681,000														255,175,000
2017	1,460,833,000														301,872,000
Thereafter	3,458,665,000														1,099,636,000
Total amortization of debt and principal repayments	6,678,073,000														1,732,588,000
Letters of credit					91,900,000
Interest expense
Interest expense	81,789,000	80,547,000
Interest income	(453,000)	(410,000)
Interest expense, net	81,336,000	80,137,000
Interest capitalized	$ 3,062,000	$ 2,536,000