Investments in Unconsolidated Joint Ventures - Summary of Financial Information (Details) - 712 Fifth Avenue [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]
Rental property, net	$ 210,343		$ 210,343		$ 214,139
Other assets	39,460		39,460		41,337
Total assets	249,803		249,803		255,476
Notes and mortgages payable, net	245,786		245,786		245,582
Other liabilities	11,796		11,796		15,000
Total liabilities	257,582		257,582		260,582
Equity	(7,779)		(7,779)		(5,106)
Total liabilities and equity	249,803		249,803		$ 255,476
Rental income	12,716	$ 12,392	25,394	$ 24,446
Tenant reimbursement income	893	1,375	2,009	2,736
Fee and other income	677	344	1,195	623
Total revenues	14,286	14,111	28,598	27,805
Operating	5,375	5,831	10,992	12,057
Depreciation and amortization	3,043	2,954	6,051	5,884
Total expenses	8,418	8,785	17,043	17,941
Operating income	5,868	5,326	11,555	9,864
Interest and other income, net	19	4	33	5
Interest and debt expense	(2,752)	(2,611)	(5,500)	(6,039)
Unrealized gain on interest rate swaps	834	1,248	834	2,020
Net income	$ 3,969	$ 3,967	$ 6,922	$ 5,850