Mortgage Notes Payable (Narrative) (Details) $ in Thousands			12 Months Ended
	Sep. 01, 2016 USD ($)	Apr. 11, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net			$ 2,063,087	$ 3,435,242
Mezzanine notes payable			$ 307,093	308,482
Final maturity date of mortgage notes			Apr. 10, 2022
Repayments of mortgage notes payable			$ 1,326,865	54,801	$ 87,758
Gains (losses) from early extinguishments of debt			$ (371)	$ (22,040)	(10,633)
Number Of Mortgage Loans Accounted For Fair Value			1	2
Outstanding balance of mortgage loans accounted for at fair value			$ 1,300,000	$ 1,500,000
Interest Expense Decrease Due To Recording Mortgage Loans At Fair Value			46,400	55,000	52,500
Cumulative Liability Related to the Fair Value of Debt Adjustment			33,800	80,200
Unamortized balance of historical fair value adjustments			33,830
Interest expense			$ 412,849	432,196	$ 455,743
Minimum [Member]
Mortgage Notes Payable [Line Items]
Number Real Estate Assets Used For Mortgage Loan Collateral			1
Fixed Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Mortgage notes payable, net			$ 2,100,000	$ 3,400,000
Contractual interest rate range, minimum			4.75%	4.75%
Contractual interest rate range, maximum			7.69%	7.69%
Contractual interest rate, weighted average interest rate			5.59%	5.69%
Variable Rate Mortgages [Member]
Mortgage Notes Payable [Line Items]
Number of variable rate mortgage loans			0	0
London Interbank Offered Rate			0.77%	0.43%
Fountain Square [Member] | Secured Debt [Member]
Mortgage Notes Payable [Line Items]
Repayments of mortgage notes payable		$ 211,300
Interest at a fixed rate		5.71%
599 Lexington Avenue | Secured Debt [Member]
Mortgage Notes Payable [Line Items]
Repayments of mortgage notes payable	$ 750,000
Interest at a fixed rate	5.57%
Effective Rate	5.41%
Gains (losses) from early extinguishments of debt	$ 400
Embarcadero Center Four [Member] | Secured Debt [Member]
Mortgage Notes Payable [Line Items]
Repayments of mortgage notes payable	$ 344,800
Interest at a fixed rate	6.10%
Effective Rate	7.02%
Gains (losses) from early extinguishments of debt	$ (700)
Consolidated Properties [Member] | 767 Fifth Avenue (the General Motors Building)
Mortgage Notes Payable [Line Items]
Ownership Percentage by Parent			60.00%
Mortgage notes payable, net			$ 1,300,000
Mezzanine notes payable			$ 306,000
Interest at a fixed rate			5.96%