Fair Value Measurements (Schedule of Derivative Instruments) (Details) - USD ($) $ in Thousands		1 Months Ended
	Aug. 11, 2025	May 31, 2027	May 31, 2026	Sep. 30, 2025	Aug. 12, 2025	Jul. 31, 2025	Dec. 31, 2024
Derivative [Line Items]
Unswapped balance				$ 2,264,306			$ 2,566,862
Forecast
Derivative [Line Items]
Basis spread on variable rate (in percent)		2.55%	2.30%
4 Union Square South
Derivative [Line Items]
Debt amount	$ 120,000
Basis spread on variable rate (in percent)	1.50%
Office | 4 Union Square South
Derivative [Line Items]
Debt amount					$ 120,000
PENN 11 mortgage loan | Office
Derivative [Line Items]
Debt amount						$ 450,000
Unsecured term loan | Interest Rate Swaps
Derivative [Line Items]
Debt amount				200,000
One Park Avenue mortgage loan | Interest Rate Swaps
Derivative [Line Items]
Debt amount				$ 500,000
Matures in May 2028 | 555 California Street | Office
Derivative [Line Items]
Equity method ownership percentage (as percent)				70.00%			70.00%
Debt amount				$ 1,200,000			$ 1,200,000
770 Broadway mortgage loan | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				700,000
Designated as Hedging Instrument
Derivative [Line Items]
Fair Value Asset				22,643			88,982
Fair Value Liability				3,459			1,023
Designated as Hedging Instrument | In-place swap | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 840,000
All-In Swapped Rate				6.03%
Fair Value Asset				$ 0			765
Fair Value Liability				1,299			0
Designated as Hedging Instrument | Forward swap | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 840,000
All-In Swapped Rate				5.56%
Fair Value Asset				$ 0			0
Fair Value Liability				1,621			0
Designated as Hedging Instrument | Unsecured term loan | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 750,000
All-In Swapped Rate				4.22%
Fair Value Asset				$ 5,231			16,217
Fair Value Liability				$ 0			0
Unswapped Balance interest rate				1.25%
Designated as Hedging Instrument | Unsecured revolving credit facility | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 575,000
All-In Swapped Rate				3.84%
Fair Value Asset				$ 6,747			18,510
Fair Value Liability				0			0
Designated as Hedging Instrument | One Park Avenue mortgage loan | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 500,000
All-In Swapped Rate				3.95%
Fair Value Asset				$ 5,564			15,243
Fair Value Liability				0			0
Unswapped balance				$ 25,000
Derivative, basis spread on variable rate				1.22%
Variable interest rate				5.37%
Cap strike rate				4.39%
Designated as Hedging Instrument | 100 West 33rd Street mortgage loan | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 480,000
All-In Swapped Rate				5.26%
Fair Value Asset				$ 0			6,808
Fair Value Liability				127			0
Designated as Hedging Instrument | 888 Seventh Avenue mortgage loan | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 200,000
All-In Swapped Rate				4.76%
Fair Value Asset				$ 1,470			5,249
Fair Value Liability				0			0
Unswapped balance				$ 47,373
Derivative, basis spread on variable rate				1.80%
Variable interest rate				6.08%
Designated as Hedging Instrument | 435 Seventh Avenue mortgage loan | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 75,000
All-In Swapped Rate				6.96%
Fair Value Asset				$ 0			0
Fair Value Liability				412			741
Designated as Hedging Instrument | PENN 11 mortgage loan | Interest Rate Swaps
Derivative [Line Items]
All-In Swapped Rate					6.35%
Fair Value Asset				0			17
Fair Value Liability				0			282
Designated as Hedging Instrument | 4 Union Square South mortgage loan | Interest Rate Swaps
Derivative [Line Items]
All-In Swapped Rate					5.64%
Fair Value Asset				0			12
Fair Value Liability				0			0
Designated as Hedging Instrument | 1290 Avenue of the Americas mortgage loan | Interest Rate Cap
Derivative [Line Items]
Notional amount and swapped balance				950,000
Fair Value Asset				3,631			25,673
Fair Value Liability				$ 0			0
Cap strike rate				1.00%
Designated as Hedging Instrument | Various mortgage loans | Interest Rate Cap
Derivative [Line Items]
Fair Value Asset				$ 0			488
Fair Value Liability				0			$ 0
Designated as Hedging Instrument | Unsecured Term Loan Expiring October 2026 | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 750,000
All-In Swapped Rate				4.22%
Unswapped Balance				$ 50,000
Designated as Hedging Instrument | Unsecured Term Loan Expiring July 2027 | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 250,000
All-In Swapped Rate				3.99%
Unswapped Balance				$ 550,000
Designated as Hedging Instrument | Unsecured Term Loan Expiring August 2027 | Interest Rate Swaps
Derivative [Line Items]
Notional amount and swapped balance				$ 50,000
All-In Swapped Rate				3.99%
Unswapped Balance				$ 750,000