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Represents the accumulated amount of amortization of a major finite-lived intangible liability class.

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Operating Lease, Annual Expense

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Significant Accounting Policies - Investments in Commercial Real Estate Properties (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jul. 01, 2022	Jun. 30, 2022
Investment in Commercial Real Estate Properties
Rental revenue decrease from amortization of acquired leases	$ 100,000	$ 200,000	$ 14,300,000	$ 100,000
Identified intangible assets (included in other assets):
Gross amount	189,680,000		189,680,000			$ 403,552,000
Accumulated amortization	(184,491,000)		(184,491,000)			(190,066,000)
Net	5,189,000		5,189,000			213,486,000
Identified intangible liabilities (included in deferred revenue):
Gross amount	205,394,000		205,394,000			361,338,000
Accumulated amortization	(202,000,000)		(202,000,000)			(212,191,000)
Net	3,394,000		$ 3,394,000			$ 149,147,000
625 Madison Avenue
Investment in Commercial Real Estate Properties
Operating lease rent							$ 20,250,000	$ 4,610,000
Write down of value in leasehold interest	$ 305,900,000
Carrying value of investment in leasehold interest					$ 0
Minimum \| Above-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)	1 year		1 year
Minimum \| Below-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)	1 year		1 year
Minimum \| In-place leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)	1 year		1 year
Maximum \| Above-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)	15 years		15 years
Maximum \| Below-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)	15 years		15 years
Maximum \| In-place leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets (in years)	15 years		15 years
Building \| Minimum
Investment in Commercial Real Estate Properties
Estimated useful life (in years)	3 years		3 years
Building \| Maximum
Investment in Commercial Real Estate Properties
Estimated useful life (in years)	40 years		40 years