Schedule III: Real estate and Accumulated depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 1,059,587
Initial cost of Land	21,593
Initial cost of Building, Leaseholds and Leasehold improvements	26,239
Costs capitalized subsequent to acquisition	981,640
Carrying amount of Land	44,971
Carring amount of Building, Leaseholds and Leasehold improvements	975,015
Construction in progress	9,486
Total	1,029,472	$ 993,927	$ 919,576	$ 911,792
Accumulated depreciation and amortization	225,533	210,025	$ 185,375	$ 160,826
Deferred debt issuance costs, net	6,325	$ 4,824
Differences Between Book and Tax Basis	200,876
Rego Park I [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	78,246
Initial cost of Land	1,647
Initial cost of Building, Leaseholds and Leasehold improvements	8,953
Costs capitalized subsequent to acquisition	51,942
Carrying amount of Land	1,647
Carring amount of Building, Leaseholds and Leasehold improvements	60,512
Construction in progress	383
Total	62,542
Accumulated depreciation and amortization	$ 29,377
Date of construction	1959
Date acquired	1992
Rego Park I [Member] | Maximum [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	39 years
Rego Park I [Member] | Minimum [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Rego Park II [Member] | New York [Member] | Apartment Tower [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial cost of Land	0
Initial cost of Building, Leaseholds and Leasehold improvements	0
Costs capitalized subsequent to acquisition	117,788
Carrying amount of Land	0
Carring amount of Building, Leaseholds and Leasehold improvements	111,027
Construction in progress	6,761
Total	117,788
Accumulated depreciation and amortization	$ 1,856
Date acquired	1992
Rego Park II [Member] | New York [Member] | Retail Space [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 263,341
Initial cost of Land	3,127
Initial cost of Building, Leaseholds and Leasehold improvements	1,467
Costs capitalized subsequent to acquisition	385,499
Carrying amount of Land	3,127
Carring amount of Building, Leaseholds and Leasehold improvements	386,582
Construction in progress	384
Total	390,093
Accumulated depreciation and amortization	$ 63,373
Date of construction	2009
Date acquired	1992
Rego Park II [Member] | Maximum [Member] | New York [Member] | Apartment Tower [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	39 years
Rego Park II [Member] | Maximum [Member] | New York [Member] | Retail Space [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Rego Park II [Member] | Minimum [Member] | New York [Member] | Apartment Tower [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Rego Park II [Member] | Minimum [Member] | New York [Member] | Retail Space [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Rego Park III [Member] | New York [Member] | Retail Space [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial cost of Land	779
Initial cost of Building, Leaseholds and Leasehold improvements	0
Costs capitalized subsequent to acquisition	2,462
Carrying amount of Land	779
Carring amount of Building, Leaseholds and Leasehold improvements	504
Construction in progress	1,958
Total	3,241
Accumulated depreciation and amortization	$ 158
Date acquired	1992
Rego Park III [Member] | Maximum [Member] | New York [Member] | Retail Space [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Rego Park III [Member] | Minimum [Member] | New York [Member] | Retail Space [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Flushing Property [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial cost of Land	0
Initial cost of Building, Leaseholds and Leasehold improvements	1,660
Costs capitalized subsequent to acquisition	(107)
Carrying amount of Land	0
Carring amount of Building, Leaseholds and Leasehold improvements	1,553
Construction in progress	0
Total	1,553
Accumulated depreciation and amortization	$ 850
Date of construction	1975
Date acquired	1992
Lexington Avenue Property [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 650,000
Initial cost of Land	14,432
Initial cost of Building, Leaseholds and Leasehold improvements	12,355
Costs capitalized subsequent to acquisition	415,547
Carrying amount of Land	27,497
Carring amount of Building, Leaseholds and Leasehold improvements	414,837
Construction in progress	0
Total	442,334
Accumulated depreciation and amortization	$ 129,919
Date of construction	2003
Date acquired	1992
Lexington Avenue Property [Member] | Maximum [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	39 years
Lexington Avenue Property [Member] | Minimum [Member] | New York [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	9 years
Paramus Property [Member] | New Jersey [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 68,000
Initial cost of Land	1,441
Initial cost of Building, Leaseholds and Leasehold improvements	0
Costs capitalized subsequent to acquisition	10,313
Carrying amount of Land	11,754
Carring amount of Building, Leaseholds and Leasehold improvements	0
Construction in progress	0
Total	11,754
Accumulated depreciation and amortization	$ 0
Date acquired	1992
Other Properties [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial cost of Land	167
Initial cost of Building, Leaseholds and Leasehold improvements	1,804
Costs capitalized subsequent to acquisition	(1,804)
Carrying amount of Land	167
Carring amount of Building, Leaseholds and Leasehold improvements	0
Construction in progress	0
Total	167
Accumulated depreciation and amortization	$ 0
Date acquired	1992