Real Estate and Accumulated Depreciation - Schedule III (Summary of Real Estate Investments) (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 [Line Items]
Encumbrances	$ 405,000
Land	193,658
Building and Improvements	504,536
Costs Capitalized Subsequent to Acquisition	66,982
Gross amount carried	765,176	$ 762,519	$ 759,487	$ 671,210
Accumulated depreciation	112,641	92,470	$ 72,656	$ 53,449
Acquired intangible assets	87,478	$ 98,118
Tax basis	727,800
Accumulated amortization	(45,200)
421 W. 54th Street - Hit Factory
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Land	4,723
Building and Improvements	1,757
Costs Capitalized Subsequent to Acquisition	(1,443)
Gross amount carried	5,037
Accumulated depreciation	337
400 E. 67th Street - Laurel Condominiums
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	44,610
Land	10,653
Building and Improvements	55,682
Costs Capitalized Subsequent to Acquisition	86
Gross amount carried	66,421
Accumulated depreciation	10,265
200 Riverside Blvd - ICON Garage
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	5,390
Land	13,787
Building and Improvements	5,510
Costs Capitalized Subsequent to Acquisition	0
Gross amount carried	19,297
Accumulated depreciation	999
9 Times Square
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	55,000
Land	54,153
Building and Improvements	76,454
Costs Capitalized Subsequent to Acquisition	26,163
Gross amount carried	156,770
Accumulated depreciation	29,372
123 William Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	140,000
Land	50,064
Building and Improvements	182,917
Costs Capitalized Subsequent to Acquisition	33,758
Gross amount carried	266,739
Accumulated depreciation	45,778
Mortgage note payable — 1140 Avenue of the Americas
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	99,000
Land	0
Building and Improvements	148,647
Costs Capitalized Subsequent to Acquisition	8,418
Gross amount carried	157,065
Accumulated depreciation	23,682
8713 Fifth Avenue
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	10,000
Land	4,730
Building and Improvements	9,245
Costs Capitalized Subsequent to Acquisition	0
Gross amount carried	13,975
Accumulated depreciation	738
196 Orchard Street
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	51,000
Land	55,548
Building and Improvements	24,324
Costs Capitalized Subsequent to Acquisition	0
Gross amount carried	79,872
Accumulated depreciation	$ 1,470
Building
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	40 years
Land Improvements
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	15 years
Minimum | Furniture and Fixtures
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	5 years
Maximum | Furniture and Fixtures
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items]
Useful life	7 years