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Investment in Unconsolidated Joint Venture - Additional Information (Detail) $ in Millions					6 Months Ended		9 Months Ended
	Jan. 01, 2027 Floors	Jun. 25, 2025 Floors	Oct. 18, 2017 USD ($)	Jun. 01, 2017 USD ($)	Jun. 30, 2025	Jun. 30, 2024	Sep. 30, 2024	Sep. 13, 2024 USD ($)	Oct. 30, 2013 USD ($)
Cravath, Swaine & Moore LLP [Member]
Schedule of Equity Method Investments [Line Items]
Lease expiration date					Aug. 31, 2024
Worldwide Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage					50.10%		50.10%		48.90%
Aggregate cost				$ 276.7					$ 220.1
Agreed upon value									1,300.0
Notes payable									$ 875.0
Additional acquire percentage				49.90%
Purchase obligation				$ 1,400.0
Mortgage notes payable				$ 875.0
Joint venture partner's right to maintain minimum ownership percentage				1.20%
Debt refinance amount			$ 1,200.0
Cash received from sale and excess proceeds from financing			446.5
Defeasance and prepayment costs			108.3
Reserved amount			$ 90.7
Debt blended rate			3.98%
Maturity date							2027-11
Interest payment								$ 0.8
Property selling percentage					100.00%
Option to purchase percentage of property					100.00%
Property purchase option period					45 days
Re-offer property selling percentage					92.50%
Worldwide Plaza [Member] \| SL Green Realty Corp. and RXR Realty LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage			48.70%
Liquidation value of property			$ 1,725.0
Worldwide Plaza [Member] \| Nomura Holdings America, Inc [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of total cash rent income					58.50%
Number of floors \| Floors		16
Mezzanine First Loan [Member] \| Worldwide Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Subsidiary borrowings loan amount								$ 190.0
Liquidation Value [Member] \| Worldwide Plaza [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage				98.80%
Liquidation Value [Member] \| Worldwide Plaza [Member] \| Nomura Holdings America, Inc [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of total annualized rental income						29.40%
Liquidation Value [Member] \| Worldwide Plaza [Member] \| Cravath, Swaine & Moore LLP [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of total annualized rental income						48.00%
Forecast [Member] \| Worldwide Plaza [Member] \| Nomura Holdings America, Inc [Member]
Schedule of Equity Method Investments [Line Items]
Number of floors \| Floors	24