Noncontrolling Interests Property Partnerships (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			$ 1,530,647,000
Capital contributions			(147,772,000)		$ (6,737,000)
Net income	$ 14,340,000	$ (17,225,000)	33,967,000		53,000
Accumulated other comprehensive income (loss)	(300,000)	(1,097,000)	2,220,000		23,011,000
Ending Balance	1,668,675,000		1,668,675,000
Property Partnerships Member
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			1,530,647,000		1,574,400,000
Capital contributions			147,772,000	[1]	5,417,000
Net income			33,967,000		53,000
Accumulated other comprehensive income (loss)			(2,272,000)		(16,134,000)
Distributions			(41,439,000)		(38,694,000)
Ending Balance	1,668,675,000	$ 1,525,042,000	1,668,675,000		$ 1,525,042,000
767 Fifth Avenue (the General Motors Building) | Property Partnerships Member
Activity of Noncontrolling Interests [Roll Forward]
Ending Balance	$ 109,576		$ 109,576

[1] Includes the contribution of the remaining unpaid principal balance of the members’ notes payable totaling $109,576 to equity in the consolidated entity that owns 767 Fifth Avenue (the General Motors Building).