Noncontrolling Interests noncontrolling interests—property partnerships table (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Beginning Balance	$ 1,530,647,000
Capital contributions	161,585,000		$ 11,951,000	$ 2,705,000
Dissolution				(4,082,000)
Net income (loss)	47,832,000		(2,068,000)	149,855,000
Accumulated other comprehensive loss	(1,922,000)		(5,256,000)	(2,982,000)
Ending Balance	1,683,760,000		1,530,647,000
Property Partnerships Member
Noncontrolling Interest [Line Items]
Beginning Balance	1,530,647,000		1,574,400,000	1,602,467,000
Capital contributions	161,585,000	[1]	10,756,000	3,758,000
Dissolution				(4,082,000)
Net income (loss)	47,832,000		(2,068,000)	144,734,000
Accumulated other comprehensive loss	(2,128,000)		(877,000)	(2,428,000)
Distributions	(54,176,000)		(51,564,000)	(170,049,000)
Ending Balance	1,683,760,000		$ 1,530,647,000	$ 1,574,400,000
767 Fifth Avenue (the general motors building) [Member] | Property Partnerships Member
Noncontrolling Interest [Line Items]
Ending Balance	$ 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).