Investments in Unconsolidated Joint Ventures - Summary of Financial Information (Details) - USD ($) $ in Thousands	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2014	Nov. 23, 2014	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2013
712 Fifth Avenue [Member]
Schedule Of Equity Method Investments [Line Items]
Rental property, net	$ 221,827		$ 214,139
Other assets	46,126		42,255
Total assets	267,953		256,394
Notes and mortgages payable	246,500		246,500
Other liabilities	30,321		15,000
Total liabilities	276,821		261,500
Equity	(8,868)		(5,106)
Total liabilities and equity	267,953		256,394
Rental income	5,118		49,382
Tenant reimbursement income	607		4,758
Fee and other income	232		1,235
Total revenue	5,957		55,375
Operating	2,586		22,956
Depreciation and amortization	1,209		11,764
General and administrative	32
Total expenses	3,827		34,720
Operating income	2,130		20,655
Unrealized gain on interest rate swaps	1,285		4,223
Interest and debt expense	(1,538)		(11,410)
Net income	$ 1,877		$ 13,468
712 Fifth Avenue [Member] | Predecessor [Member]
Schedule Of Equity Method Investments [Line Items]
Rental income		$ 41,710			$ 41,166
Tenant reimbursement income		4,282			4,311
Fee and other income		1,274			1,785
Total revenue		47,266			47,262
Operating		20,826			22,306
Depreciation and amortization		10,127			10,009
General and administrative		182			194
Total expenses		31,135			32,509
Operating income		16,131			14,753
Unrealized gain on interest rate swaps		5,249			10,031
Interest and debt expense		(13,098)			(14,517)
Net income		8,282			10,267
Oder-Center, Germany [Member]
Schedule Of Equity Method Investments [Line Items]
Rental property, net				$ 6,626
Other assets				1,228
Total assets				7,854
Notes and mortgages payable				24,143
Other liabilities				245
Total liabilities				24,388
Equity				(16,534)
Total liabilities and equity				7,854
Rental income				4,458
Fee and other income				60
Total revenue				4,518
Operating				625
Depreciation and amortization				401
Total expenses				1,026
Operating income				3,492
Interest and debt expense				(1,186)
Net income				2,285
Income tax expense				$ (21)
1325 Avenue of the Americas [Member] | Predecessor [Member]
Schedule Of Equity Method Investments [Line Items]
Rental property, net					209,455
Other assets					56,479
Total assets					265,934
Notes and mortgages payable					220,000
Other liabilities					5,450
Total liabilities					225,450
Equity					40,484
Total liabilities and equity					265,934
Rental income		33,693			33,397
Tenant reimbursement income		4,629			5,186
Fee and other income		1,472			1,203
Total revenue		39,794			39,786
Operating		21,381			23,667
Depreciation and amortization		7,959			7,830
General and administrative		215			238
Total expenses		29,555			31,735
Operating income		10,239			8,051
Interest and debt expense		(10,039)			(11,150)
Net income		200			(3,099)
900 Third Avenue [Member] | Predecessor [Member]
Schedule Of Equity Method Investments [Line Items]
Rental property, net					135,886
Other assets					35,288
Total assets					171,174
Notes and mortgages payable					274,337
Other liabilities					30,797
Total liabilities					305,134
Equity					(133,960)
Total liabilities and equity					171,174
Rental income		32,269			33,601
Tenant reimbursement income		3,001			3,036
Fee and other income		630			732
Total revenue		35,900			37,369
Operating		15,818			17,130
Depreciation and amortization		6,085			6,349
General and administrative		113			156
Total expenses		22,016			23,635
Operating income		13,884			13,734
Unrealized gain on interest rate swaps		5,759			9,985
Interest and debt expense		(13,269)			(14,872)
Net income		$ 6,374			$ 8,847