Schedule III: Real estate and Accumulated depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	$ 1,096,544
Initial cost of Land	19,985
Initial cost of Building and Leasehold improvements	24,435
Costs capitalized subsequent to acquisition	1,025,006
Carrying amount of Land	33,050
Carrying amount of Buildings and Leasehold improvements	1,014,525
Development and Construction in progress	21,851
Total	1,069,426	$ 1,071,043	$ 1,041,342	$ 1,027,691
Accumulated Depreciation and Amortization	370,557	$ 350,122	$ 324,499	$ 297,421
Deferred debt issuance costs, net	6,931
Differences between book and tax basis	144,100
New York | Rego Park I
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	0
Initial cost of Land	1,647
Initial cost of Building and Leasehold improvements	8,953
Costs capitalized subsequent to acquisition	90,499
Carrying amount of Land	1,647
Carrying amount of Buildings and Leasehold improvements	87,988
Development and Construction in progress	11,464
Total	101,099
Accumulated Depreciation and Amortization	$ 41,036
Date of construction	1959
Date acquired	1992
New York | Rego Park I | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	3 years
New York | Rego Park I | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	39 years
New York | Rego Park II | Retail space
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	$ 202,544
Initial cost of Land	3,127
Initial cost of Building and Leasehold improvements	1,467
Costs capitalized subsequent to acquisition	390,067
Carrying amount of Land	3,127
Carrying amount of Buildings and Leasehold improvements	390,090
Development and Construction in progress	1,444
Total	394,661
Accumulated Depreciation and Amortization	$ 122,234
Date of construction	2009
Date acquired	1992
New York | Rego Park II | Retail space | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	3 years
New York | Rego Park II | Retail space | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	40 years
New York | The Alexander apartment tower
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	$ 94,000
Initial cost of Land	0
Initial cost of Building and Leasehold improvements	0
Costs capitalized subsequent to acquisition	119,112
Carrying amount of Land	0
Carrying amount of Buildings and Leasehold improvements	119,112
Development and Construction in progress	0
Total	119,112
Accumulated Depreciation and Amortization	$ 24,499
Date of construction	2016
Date acquired	1992
New York | The Alexander apartment tower | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	3 years
New York | The Alexander apartment tower | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	39 years
New York | Rego Park III
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	$ 0
Initial cost of Land	779
Initial cost of Building and Leasehold improvements	0
Costs capitalized subsequent to acquisition	8,256
Carrying amount of Land	779
Carrying amount of Buildings and Leasehold improvements	526
Development and Construction in progress	7,730
Total	9,035
Accumulated Depreciation and Amortization	$ 361
Date acquired	1992
New York | Rego Park III | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	5 years
New York | Rego Park III | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	15 years
New York | Flushing
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	$ 0
Initial cost of Land	0
Initial cost of Building and Leasehold improvements	1,660
Costs capitalized subsequent to acquisition	(107)
Carrying amount of Land	0
Carrying amount of Buildings and Leasehold improvements	1,553
Development and Construction in progress	0
Total	1,553
Accumulated Depreciation and Amortization	$ 1,205
Date of construction	1975
Date acquired	1992
New York | Lexington Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Encumbrances	$ 800,000
Initial cost of Land	14,432
Initial cost of Building and Leasehold improvements	12,355
Costs capitalized subsequent to acquisition	417,179
Carrying amount of Land	27,497
Carrying amount of Buildings and Leasehold improvements	415,256
Development and Construction in progress	1,213
Total	443,966
Accumulated Depreciation and Amortization	$ 181,222
Date of construction	2003
Date acquired	1992
New York | Lexington Avenue | Minimum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	9 years
New York | Lexington Avenue | Maximum
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation
Life on which Depreciation in Latest Income Statement is Computed	39 years