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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]
Real estate, net	$ 206,617		$ 206,617		$ 207,632
Other assets	51,374		51,374		40,701
Total assets	257,991		257,991		248,333
Notes and mortgages payable, net	295,949		295,949		245,990
Other liabilities	4,447		4,447		8,783
Total liabilities	300,396		300,396		254,773
Equity	(42,405)		(42,405)		(6,440)
Total liabilities and equity	257,991		257,991		$ 248,333
Rental income	12,713	$ 12,716	25,658	$ 25,394
Tenant reimbursement income	1,209	893	2,517	2,009
Fee and other income	468	677	594	1,195
Total revenues	14,390	14,286	28,769	28,598
Operating expenses	6,102	5,375	12,068	10,992
Depreciation and amortization	3,075	3,043	5,995	6,051
Total expenses	9,177	8,418	18,063	17,043
Operating income	5,213	5,868	10,706	11,555
Interest and other income, net	48	19	72	33
Interest and debt expense	(3,126)	(2,752)	(5,951)	(5,500)
Unrealized gain on interest rate swaps	728	834	1,896	834
Net income	$ 2,863	$ 3,969	$ 6,723	$ 6,922