Real Estate (Narrative) (Details) $ in Thousands													3 Months Ended	4 Months Ended	5 Months Ended	7 Months Ended	8 Months Ended	10 Months Ended	12 Months Ended
	Nov. 08, 2022 USD ($) ft² floor	Oct. 19, 2022 ft² Building	Sep. 16, 2022 USD ($) ft²	Sep. 15, 2022 USD ($) land_parcel	Aug. 30, 2022 USD ($) ft²	Jul. 01, 2022 ft² Building	Jun. 15, 2022 USD ($) ft² Building	May 17, 2022 USD ($) ft² floor	Apr. 27, 2022 ft² Building	Apr. 07, 2022 USD ($)	Mar. 31, 2022 USD ($) ft²	Apr. 19, 2021 USD ($) a ft²	Mar. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) ft²	Jun. 14, 2022 USD ($)	Dec. 31, 2022 USD ($) ft²	Aug. 29, 2022 USD ($)	Nov. 07, 2022 USD ($)	Dec. 31, 2022 USD ($) ft²	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 23, 2022 ft²	Dec. 01, 2022 ft²	Nov. 30, 2022 ft²	Sep. 12, 2022 ft²	Sep. 08, 2022 ft²	Jun. 29, 2022 ft²	May 13, 2022 ft²	Apr. 29, 2022 ft²	May 09, 2019 ft²
Real Estate Properties [Line Items]
Unsecured term loan								$ 730,000						$ 730,000		$ 730,000			$ 730,000	$ 0
Total revenue																			3,108,581	2,888,621	$ 2,765,686
Net income																			1,020,584	631,932	1,018,691
Proceeds from sales of real estate																			834,770	179,887	519,303
Interest and Other Income																			11,940	5,704	5,953
Other income - assignment fee																			$ 6,624	0	0
Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²														3,200,000		3,200,000			3,200,000
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Unsecured term loan														$ 730,000		$ 730,000			$ 730,000	0
Total revenue																			3,108,581	2,888,621	2,765,686
Net income																			1,032,122	641,771	1,038,739
Proceeds from sales of real estate																			834,770	179,887	519,303
Interest and Other Income																			11,940	5,704	5,953
Other income - assignment fee																			$ 6,624	0	0
Madison Centre
Real Estate Properties [Line Items]
Noncash or Part Noncash Acquisition, Value of Assets Acquired								$ 724,300
Net Rentable Area (in sf) | ft²								755,000
Number of floors | floor								37
Total revenue																32,000
Net income																$ 2,100
125 Broadway
Real Estate Properties [Line Items]
Payments to Acquire Real Estate			$ 592,400
Net Rentable Area (in sf) | ft²			271,000
Total revenue														11,400
Net income														$ 3,300
195 West Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²											63,500
Net income													$ 400							500	(800)
Contractual Sales Price											$ 37,700
Proceeds from sales of real estate											35,400
Gains (Losses) on Sales of Investment Real Estate											22,700
195 West Street | Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Gains (Losses) on Sales of Investment Real Estate											$ 23,400
11251 Roger Bacon Drive
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²												65,000
Asset Acquisition, Price of Acquisition, Expected												$ 5,600
Interest and Other Income										$ 6,900
Other income - assignment fee										$ 6,600
Area of Land | a												2.6
Virginia 95 Office Park
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²							733,000
Net income															$ 2,300					7,000	7,800
Contractual Sales Price							$ 127,500
Proceeds from sales of real estate							121,900
Gains (Losses) on Sales of Investment Real Estate							$ 96,200
Number of buildings | Building							11
Virginia 95 Office Park | Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Gains (Losses) on Sales of Investment Real Estate							$ 99,500
601 Massachusetts Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²					479,000
Net income																	$ 14,900			22,400	21,800
Contractual Sales Price					$ 531,000
Proceeds from sales of real estate					512,300
Gains (Losses) on Sales of Investment Real Estate					237,400
601 Massachusetts Avenue | Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Gains (Losses) on Sales of Investment Real Estate					$ 237,500
Loudoun County Land
Real Estate Properties [Line Items]
Contractual Sales Price				$ 27,000
Proceeds from sales of real estate				25,600
Gains (Losses) on Sales of Investment Real Estate				$ 24,400
Parcels of undeveloped land | land_parcel				2
The Avant at Reston Town Center
Real Estate Properties [Line Items]
Net income																		$ 4,100		$ 4,000	$ 4,000
The Avant at Reston Town Center | Residential Building
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²	329,000
Number of floors | floor	15
Contractual Sales Price	$ 141,000
Proceeds from sales of real estate	139,600
Gains (Losses) on Sales of Investment Real Estate	$ 55,600
Number of Units in Real Estate Property	359
The Avant Retail | Retail Site [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²	26,000
290 Binney Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									566,000
Lessor, Operating Lease, Lease Not yet Commenced, Description									15-year
Kendall Center future development | Scenario, Plan
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									1,100,000
Number of buildings | Building									2
Kendall Center future development | Scenario, Plan | Residential Building
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									400,000
2100 Pennsylvania Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																													480,000
Reston Next Office Phase II
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																												90,000
325 Main Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																											414,000			115,000
140 Kendrick Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²						388,000
Number of buildings | Building						3
140 Kendrick - Building A
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²						90,000
Number of buildings | Building						1
140 Kendrick - Building A | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²						104,000
300 Binney Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																										195,000
300 Binney Street | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																										240,000
760 Boylston Street [Member] | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																									118,000
Reston Next
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²		1,100,000
Number of buildings | Building		2
105 Carnegie Center
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																								70,000
105 Carnegie Center | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																								73,000
2096 Gaither Road
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																							50,000
880 Winter Street [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																						244,000