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Real Estate (Narrative) (Details) $ in Thousands		3 Months Ended		6 Months Ended	9 Months Ended
	Jun. 27, 2025 USD ($) ft²	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Jun. 26, 2025 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Jul. 31, 2025 ft² floor	Jul. 17, 2025 ft²	Jul. 01, 2025 ft²	Mar. 31, 2025 ft²	Jan. 16, 2025 ft²
Real Estate Properties [Line Items]
Gains on sales of real estate		$ 1,932	$ 517		$ 20,322	$ 517
Net Income (Loss)		(116,840)	108,452		89,206	322,005
Impairment loss		68,901	0		68,901	13,615
Wholly Owned Properties
Real Estate Properties [Line Items]
Impairment loss		68,900
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Gains on sales of real estate		1,932	517		20,421	517
Net Income (Loss)		(112,224)	110,156		97,327	327,109
Impairment loss		65,988	0		65,988	13,615
Boston Properties Limited Partnership | Wholly Owned Properties
Real Estate Properties [Line Items]
Impairment loss		$ 66,000
Reston Next Retail
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²											30,000
1050 Winter Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									162,000	162,000
17 Hartwell Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²	30,000
Gains on sales of real estate					18,400
Proceeds from Sale, Real Estate, Held-for-Investment	$ 21,800
Net Income (Loss)			$ (100)	$ (300)		$ 200
17 Hartwell Avenue | Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Gains on sales of real estate					$ 18,500
Reston Next Office Phase II
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²								87,000
343 Madison Avenue | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²							930,000
Number of floors | floor							46

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