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, 2016	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
712 Fifth Avenue [Member]
Schedule Of Equity Method Investments [Line Items]
Rental property, net			$ 207,632		$ 214,139
Other assets			40,701		41,337
Total assets			248,333		255,476
Notes and mortgages payable, net			245,990		245,582
Other liabilities			8,783		15,000
Total liabilities			254,773		260,582
Equity			(6,440)		(5,106)
Total liabilities and equity			248,333		255,476
Rental income	$ 5,118		50,228		49,382
Tenant reimbursement income	607		4,495		4,758
Fee and other income	231		1,850		1,235
Total revenues	5,956		56,573		55,375
Operating	2,586		22,826		22,956
Depreciation and amortization	1,209		12,127		11,764
General and administrative	32
Total expenses	3,827		34,953		34,720
Operating income	2,129		21,620		20,655
Interest and other income	1		68		15
Interest and debt expense	(1,538)		(11,128)		(11,425)
Unrealized gain on interest rate swaps	1,285		4,109		4,223
Net income	$ 1,877		$ 14,669		$ 13,468
712 Fifth Avenue [Member] | Predecessor [Member]
Schedule Of Equity Method Investments [Line Items]
Rental income		$ 41,710
Tenant reimbursement income		4,282
Fee and other income		1,269
Total revenues		47,261
Operating		20,826
Depreciation and amortization		10,127
General and administrative		182
Total expenses		31,135
Operating income		16,126
Interest and other income		5
Interest and debt expense		(13,098)
Unrealized gain on interest rate swaps		5,249
Net income		$ 8,282
Oder-Center, Germany [Member]
Schedule Of Equity Method Investments [Line Items]
Rental property, net				$ 6,271		$ 6,626
Other assets				1,150		1,228
Total assets				7,421		7,854
Notes and mortgages payable, net				23,073		24,143
Other liabilities				323		245
Total liabilities				23,396		24,388
Equity				(15,975)		(16,534)
Total liabilities and equity				7,421		7,854
Rental income				4,192		4,458
Fee and other income				32		60
Total revenues				4,224		4,518
Operating				844		625
Depreciation and amortization				382		401
Total expenses				1,226		1,026
Operating income				2,998		3,492
Interest and debt expense				(1,084)		(1,186)
Income tax expense				(10)		(21)
Net income				$ 1,904		$ 2,285