Noncontrolling Interests Property Partnerships (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			$ 1,530,647,000
Capital contributions			(133,072,000)		$ (5,040,000)
Net income	$ 15,203,000	$ 6,814,000	19,627,000		17,278,000
Accumulated other comprehensive income (loss)	2,738,000	8,681,000	2,520,000		24,108,000
Ending Balance	1,653,981,000		1,653,981,000
Property Partnerships Member
Activity of Noncontrolling Interests [Roll Forward]
Beginning Balance			1,530,647,000		1,574,400,000
Capital contributions			133,072,000	[1]	3,720,000
Net income			19,627,000		17,278,000
Accumulated other comprehensive income (loss)			(2,416,000)		(16,547,000)
Distributions			(26,949,000)		(25,914,000)
Ending Balance	1,653,981,000	$ 1,552,937,000	1,653,981,000		$ 1,552,937,000
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).