Real Estate (Narrative) (Details) $ in Thousands											1 Months Ended	2 Months Ended	3 Months Ended		4 Months Ended	8 Months Ended	9 Months Ended
	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 ($) ft²	Apr. 27, 2022 ft² Building	Apr. 07, 2022 USD ($)	Mar. 31, 2022 USD ($) ft²	Apr. 19, 2021 USD ($) a ft²	Sep. 30, 2022 USD ($) ft²	Aug. 30, 2022 USD ($) ft²	Sep. 30, 2022 USD ($) ft²	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) ft²	Aug. 30, 2022 USD ($) ft²	Sep. 30, 2022 USD ($) ft²	Sep. 30, 2021 USD ($)	Sep. 12, 2022 ft²	Jul. 15, 2022 ft²	Jun. 29, 2022 ft²	May 13, 2022 ft²	Apr. 29, 2022 ft²	Dec. 31, 2021 USD ($)	May 09, 2019 ft²
Real Estate Properties [Line Items]
Total revenue													$ 790,523	$ 730,056			$ 2,318,757	$ 2,157,558
Net income													420,661	139,250			864,861	408,647
Proceeds from sales of real estate																	695,231	0
Interest and Other Income													3,728	1,520			6,151	4,140
Unsecured term loan						$ 730,000					$ 730,000		$ 730,000		$ 730,000		730,000							$ 0
Other income - assignment fee																	$ 6,624	0
Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²											4,400,000		4,400,000		4,400,000		4,400,000
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Total revenue													$ 790,523	730,056			$ 2,318,757	2,157,558
Net income													422,379	140,985			874,091	415,207
Proceeds from sales of real estate																	695,231	0
Interest and Other Income													3,728	1,520			6,151	4,140
Unsecured term loan											$ 730,000		$ 730,000		$ 730,000		730,000							$ 0
Other income - assignment fee																	6,624	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						37
Total revenue															18,800
Net income															$ 1,300
125 Broadway
Real Estate Properties [Line Items]
Noncash or Part Noncash Acquisition, Value of Assets Acquired	$ 592,400
Net Rentable Area (in sf) | ft²	271,000
Total revenue											1,600
Net income											$ 400
195 West Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²									63,500
Net income														400			400	200
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
Area of Land | a										2.6
Leased percentage										100.00%
Other income - assignment fee								$ 6,600
Virginia 95 Office Park
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²					733,000
Net income														1,800			$ 2,300	5,900
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									479,000				479,000
Net income												$ 3,600		$ 5,600		$ 14,900		$ 16,700
Contractual Sales Price			$ 531,000									$ 531,000				$ 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
290 Binney Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²							570,000
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
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
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
880 Winter Street [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																				244,000
760 Boylston Street [Member] | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²																			118,000