Corporate Indebtedness (Details) (USD $)			1 Months Ended			1 Months Ended		9 Months Ended		1 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Mar. 31, 2014 2012 Credit Facility	Sep. 30, 2014 2012 Credit Facility	Nov. 30, 2012 2012 Credit Facility	Mar. 31, 2014 Revolving credit facility extension	Sep. 30, 2014 Revolving credit facility	Sep. 30, 2014 Revolving credit facility Maximum	Sep. 30, 2014 Revolving credit facility Minimum	Mar. 31, 2014 Term loan	Sep. 30, 2014 Term loan	Jun. 30, 2005 Trust Preferred Securities	Sep. 30, 2014 Trust Preferred Securities	Sep. 30, 2014 LIBOR Revolving credit facility	Sep. 30, 2014 LIBOR Revolving credit facility Maximum	Sep. 30, 2014 LIBOR Revolving credit facility Minimum	Sep. 30, 2014 LIBOR Term loan	Sep. 30, 2014 LIBOR Term loan Maximum	Sep. 30, 2014 LIBOR Term loan Minimum	Sep. 30, 2014 LIBOR Trust Preferred Securities
Mortgages and Other Loans Payable
Face amount of loan					$ 1,600,000,000.0
Increase in maximum borrowing capacity										383,000,000
Maximum borrowing capacity						1,200,000,000.0				783,000,000
Decrease in basis spread on variable rate (percent)						0.25%
Number of extension options (extensions)						2
Extension option available						6 months
Extension fee (percent)						0.10%
Maximum borrowing capacity, optional expansion						1,500,000,000.0
Effective Rate (as a percent)							1.61%				1.64%
Interest rate added to base rate (as a percent)														1.45%	1.75%	1.00%	1.40%	1.90%	0.95%	1.25%
Fee on the unused balance, payable quarterly in arrears (as a percent)								0.35%	0.15%
Facility fee on total commitments, payable quarterly in arrears (as a percent)									0.30%
Letters of credit				113,300,000
Outstanding under line of credit facility	244,000,000	220,000,000					244,000,000				783,000,000
Ability to borrow under line of credit facility				800,000,000
Debt origination and legal costs			2,800,000
Debt instrument issued, value												$ 100,000,000.0
Coupon Rate (as a percent)													5.61%
Number of years for which securities will bear fixed rate of interest												10 years