Schedule III: Real estate and Accumulated depreciation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 1,032,780
Initial cost of Land	21,593
Initial cost of Building, Leaseholds and Leasehold improvements	26,239
Costs capitalized subsequent to acquisition	946,095
Carrying amount of Land	44,971
Carring amount of Building, Leaseholds and Leasehold improvements	873,667
Construction in progress	75,289
Total	993,927	919,576	911,792	906,907
Accumulated depreciation and amortization	210,025	185,375	160,826	136,460
Differences Between Book and Tax Basis	204,815
Lexington Avenue Property [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	620,000
Initial cost of Land	14,432
Initial cost of Building, Leaseholds and Leasehold improvements	12,355
Costs capitalized subsequent to acquisition	426,691
Carrying amount of Land	27,497
Carring amount of Building, Leaseholds and Leasehold improvements	425,981
Construction in progress	0
Total	453,478
Accumulated depreciation and amortization	128,798
Date of construction	2003
Date acquired	1992
Lexington Avenue Property [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	39 years
Lexington Avenue Property [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	9 years
Rego Park 1 Shopping [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	50,553
Carrying amount of Land	1,647
Carring amount of Building, Leaseholds and Leasehold improvements	59,370
Construction in progress	136
Total	61,153
Accumulated depreciation and amortization	27,569
Date of construction	1959
Date acquired	1992
Rego Park 1 Shopping [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	39 years
Rego Park 1 Shopping [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Rego Park 2 Residential Property [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	73,327
Carrying amount of Land	0
Carring amount of Building, Leaseholds and Leasehold improvements	0
Construction in progress	73,327
Total	73,327
Accumulated depreciation and amortization	0
Date acquired	1992
Rego Park 2 Retail Property [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	266,534
Initial cost of Land	3,127
Initial cost of Building, Leaseholds and Leasehold improvements	1,467
Costs capitalized subsequent to acquisition	384,926
Carrying amount of Land	3,127
Carring amount of Building, Leaseholds and Leasehold improvements	386,260
Construction in progress	133
Total	389,520
Accumulated depreciation and amortization	52,747
Date of construction	2009
Date acquired	1992
Rego Park 2 Retail Property [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Rego Park 2 Retail Property [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Paramus Property [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
Flushing Property [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	791
Date of construction	1975
Date acquired	1992
Rego Park 3 Property [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	2,196
Carrying amount of Land	779
Carring amount of Building, Leaseholds and Leasehold improvements	503
Construction in progress	1,693
Total	2,975
Accumulated depreciation and amortization	120
Date acquired	1992
Rego Park 3 Property [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Rego Park 3 Property [Member] | Minimum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	5 years
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