Investment in Unconsolidated Joint Ventures (Narrative) (Details) $ in Thousands																			1 Months Ended	4 Months Ended			12 Months Ended
		Dec. 31, 2022 USD ($)	Dec. 23, 2022 ft² loanExtension	Dec. 22, 2022 USD ($) loanExtension	Dec. 07, 2022 ft²	Dec. 06, 2022 USD ($) loanExtension	Nov. 17, 2022 USD ($) ft² floor	Sep. 09, 2022 USD ($) ft²	Sep. 08, 2022 USD ($)	Sep. 01, 2022 USD ($) ft²	Aug. 08, 2022 USD ($) ft²	Aug. 07, 2022 USD ($)	Jun. 17, 2022 USD ($)	Jun. 16, 2022 USD ($) ft²	May 13, 2022 USD ($) loanExtension years	Apr. 18, 2022 USD ($) ft²	Mar. 28, 2022 USD ($) years loanExtension	Mar. 27, 2022 USD ($) years loanExtension	Dec. 31, 2022 USD ($)	Sep. 06, 2023	Sep. 05, 2023	Apr. 30, 2023	Dec. 31, 2022 USD ($)		Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)		Feb. 02, 2022 ft²	Jan. 18, 2022 ft²
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)		$ 3,272,368																	$ 3,272,368				$ 3,272,368		$ 3,267,914
Debt Instrument, Basis Spread on Variable Rate		0.775%
Payment for Debt Extinguishment or Debt Prepayment Cost																							0		43,036	$ 0
Losses from early extinguishment of debt																							0		(45,182)	0
Payments to Acquire Equity Method Investments																							277,581		98,152	172,436
Assumption of mortgage notes payable																							$ 0		200,311	0
Gateway Commons Complex [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[1]	50.00%																	50.00%				50.00%
Gateway Commons Complex [Member] | 651 Gateway | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage																													50.00%
Platform 16
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[2]	55.00%																	55.00%				55.00%
Platform 16 | Platform 16 | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage																												55.00%
Net Rentable Area (in sf) | ft²																												1,100,000
BP/CRF Metropolitan Square LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		20.00%																	20.00%				20.00%
BP/CRF Metropolitan Square LLC [Member] | Metropolitan Square | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage																	20.00%
Net Rentable Area (in sf) | ft²										657,000
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)																	$ 420,000	$ 294,100
Debt Instrument, Description of Variable Rate Basis																		the greater of (x) LIBOR or (y) 0.65%
Debt Instrument, Basis Spread on Variable Rate																	2.75%	4.75%
Number of extensions | loanExtension																	3	2
Extension Option (in years) | years																	1	1
Payment for Debt Extinguishment or Debt Prepayment Cost																	$ 0
Losses from early extinguishment of debt																	(1,300)
Proceeds from mortgage notes payable																	100,500
BP/CRF Metropolitan Square LLC [Member] | Metropolitan Square | Unconsolidated Properties | Interest Rate Cap
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Description of Variable Rate Basis										SOFR
Derivative, Notional Amount										$ 420,000
Derivative, Cap Interest Rate										4.50%
Residential Tower Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%																	50.00%				50.00%
Residential Tower Developer LLC [Member] | Hub50House [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage																50.00%
Proceeds from mortgage notes payable													$ 6,800
Residential Tower Developer LLC [Member] | Hub50House [Member] | Unconsolidated Properties | Interest Rate Swap
Schedule of Equity Method Investments [Line Items]
Derivative, Notional Amount													$ 185,000
Derivative, Forward Interest Rate													4.432%
Residential Tower Developer LLC [Member] | Hub50House [Member] | Unconsolidated Properties | Adjustable Rate Loans
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)													$ 185,000	$ 176,700		$ 176,500
Debt Instrument, Basis Spread on Variable Rate													1.35%			2.00%
PR II BXP Reston Gateway LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[3]	20.00%																	20.00%				20.00%
751 Gateway Holdings LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[1]	49.00%																	49.00%				49.00%
BNY Tower Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[4]	50.00%																	50.00%				50.00%
BNY Tower Holdings LLC [Member] | Dock 72 [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage											50.00%
Net Rentable Area (in sf) | ft²											669,000
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)				$ 198,400							$ 198,400	$ 198,400
Debt Instrument, Description of Variable Rate Basis				the greater of (x) SOFR or (y) 0.25%							the greater of (x) SOFR or (y) 0.25%	LIBOR
Debt Instrument, Basis Spread on Variable Rate				2.50%							3.10%	3.35%
Debt Instrument, Interest Rate, Stated Percentage				0.25%							0.25%
Debt instrument, borrowing capacity												$ 250,000
Impairment loss on investment																			$ 50,700
Capitalization Rate																			5.75%
Investment in Unconsolidated Joint Venture, Measurement Input																			7.00%
Equity Method Investment, impairment information																			The Company determined that its valuation of the investment was categorized within Level 3 of the fair value hierarchy, as it utilized significant unobservable inputs in its assessment including an exit capitalization rate of 5.75%, a discount rate on the Company’s equity investment (the property is encumbered by mortgage debt) of 7.0% and leasing the currently available space over the period of 2023-2026.
Safeco Plaza REIT LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	[5]	33.67%																	33.67%				33.67%
Safeco Plaza REIT LLC | Safeco Plaza | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage								33.67%
Net Rentable Area (in sf) | ft²								765,000
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)									$ 250,000
Debt Instrument, Description of Variable Rate Basis								the greater of (x) 2.35% or (y) SOFR	the greater of (x) 2.35% or (y) LIBOR
Debt Instrument, Basis Spread on Variable Rate								2.32%	2.20%
Safeco Plaza REIT LLC | Safeco Plaza | Unconsolidated Properties | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage								2.35%	2.35%
Safeco Plaza REIT LLC | Safeco Plaza | Unconsolidated Properties | Interest Rate Cap
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Description of Variable Rate Basis								SOFR
Derivative, Notional Amount								$ 250,000
Derivative, Cap Interest Rate								2.50%
200 Fifth Avenue JV LLC
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		26.69%																	26.69%				26.69%
200 Fifth Avenue JV LLC | 200 Fifth Avenue | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage							26.69%
Net Rentable Area (in sf) | ft²							855,000
Debt Instrument, Basis Spread on Variable Rate							1.30%
Noncash or Part Noncash Acquisition, Value of Assets Acquired							$ 280,200
Payments to Acquire Equity Method Investments							120,100
Assumption of mortgage notes payable							$ 160,100
Number of floors | floor							14
200 Fifth Avenue JV LLC | 200 Fifth Avenue | Unconsolidated Properties | Interest Rate Swap
Schedule of Equity Method Investments [Line Items]
Derivative, Notional Amount							$ 600,000
Derivative, Forward Interest Rate							4.34%
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%																	50.00%				50.00%
Square 407 Limited Partnership [Member] | Market Square North | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage					50.00%
Net Rentable Area (in sf) | ft²					418,000
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)						$ 125,000
Debt Instrument, Description of Variable Rate Basis					the greater of (1) the sum of (x) the “benchmark rate”, (y) 2.30% and (z) the adjustment applicable to such “benchmark rate” (approximately 0.11% for Term SOFR), or (2) 2.80%	the greater of (x) LIBOR or (y) 0.50%,
Debt Instrument, Basis Spread on Variable Rate						2.30%
Number of extensions | loanExtension						1
Extension Option (in years)					1	1
Square 407 Limited Partnership [Member] | Market Square North | Unconsolidated Properties | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					2.80%
Podium Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage		50.00%																	50.00%				50.00%
Joint Venture Partner [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Interest in Joint Venture															$ 500
Joint Venture Partner [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties | Scenario, Plan
Schedule of Equity Method Investments [Line Items]
Ownership Percentage															80.00%
Payments to Acquire Interest in Joint Venture															$ 58,700
Joint Venture Partner [Member] | 751 Gateway Holdings LLC | 751 Gateway | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage														51.00%
Contribution of Property														$ 53,900
Payments to Acquire Interest in Joint Venture														$ 4,900
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)		$ 4,022,746																	$ 4,022,746				$ 4,022,746		3,214,961
Losses from early extinguishment of debt																							(1,327)		0	0
Impairment loss on investment																							$ (50,705)	[6]	$ 0	$ (60,524)	[6]
Unconsolidated Joint Ventures [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Contribution of Property															11,300
Unconsolidated Joint Ventures [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties | Scenario, Plan
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Interest in Joint Venture															$ 3,500
Unconsolidated Joint Ventures [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties | Adjustable Rate Loans
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Description of Variable Rate Basis															SOFR
Debt Instrument, Basis Spread on Variable Rate															2.00%
Number of extensions | loanExtension															2
Extension Option (in years) | years															1
Debt Instrument, Unused Borrowing Capacity, Amount															$ 140,000
Unconsolidated Joint Ventures [Member] | 751 Gateway Holdings LLC | 751 Gateway | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage														49.00%
Contribution of Property														$ 53,900
Payments to Acquire Interest in Joint Venture														$ 2,600
Unconsolidated Joint Ventures [Member] | Podium Developer LLC [Member] | The Hub on Causeway - Podium | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			50.00%
Net Rentable Area (in sf) | ft²			380,000
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)				$ 174,300
Unconsolidated Joint Ventures [Member] | Podium Developer LLC [Member] | The Hub on Causeway - Podium | Unconsolidated Properties | London Interbank Offered Rate (LIBOR)
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.25%																		2.25%
Unconsolidated Joint Ventures [Member] | Podium Developer LLC [Member] | The Hub on Causeway - Podium | Unconsolidated Properties | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate																				2.35%
Unconsolidated Joint Ventures [Member] | Office Tower Developer LLC | 100 Causeway Street [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			50.00%
Net Rentable Area (in sf) | ft²			630,000
Mortgage notes payable, net (amounts related to VIEs of $3,272,368 and $3,267,914 at December 31, 2022 and December 31, 2021, respectively)				$ 337,600
Number of extensions | loanExtension			2	2
Extension Option (in years)			1	1
Unconsolidated Joint Ventures [Member] | Office Tower Developer LLC | 100 Causeway Street [Member] | Unconsolidated Properties | London Interbank Offered Rate (LIBOR)
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate				1.50%																		1.50%
Unconsolidated Joint Ventures [Member] | Office Tower Developer LLC | 100 Causeway Street [Member] | Unconsolidated Properties | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Basis Spread on Variable Rate																					1.60%
Company's Share [Member] | BP/CRF Metropolitan Square LLC [Member] | Metropolitan Square
Schedule of Equity Method Investments [Line Items]
Proceeds from mortgage notes payable																	$ 20,100
Company's Share [Member] | Residential Tower Developer LLC [Member] | Hub50House [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Proceeds from mortgage notes payable													$ 3,400
Company's Share [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Ownership Percentage															96.00%
Company's Share [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties | Scenario, Plan
Schedule of Equity Method Investments [Line Items]
Ownership Percentage															20.00%
Construction | Gateway Commons Complex [Member] | 651 Gateway | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²																													327,000
Construction | Platform 16 | Platform 16 | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²																												390,000
Construction | 751 Gateway Holdings LLC | 751 Gateway | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²														231,000
Construction | Unconsolidated Joint Ventures [Member] | PR II BXP Reston Gateway LLC | Reston Next Residential | Unconsolidated Properties | Scenario, Plan
Schedule of Equity Method Investments [Line Items]
Number of Units in Real Estate Property															508
Residential Building | Residential Tower Developer LLC [Member] | Hub50House [Member] | Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Net Rentable Area (in sf) | ft²																320,000
Number of Units in Real Estate Property																440

[1] On June 16, 2022, in accordance with the Gateway Commons joint venture agreement, 751 Gateway was segregated into a new single-purpose joint venture.

[2] This entity is a VIE (See Note 2).

[3] The Company’s partner will fund required capital until its aggregate investment is approximately 80% of all capital contributions; thereafter, the partners will fund required capital according to their percentage interests.

[4] This property includes net equity balances from the amenity joint venture.

[5] The Company’s ownership includes (1) a 33.0% direct interest in the joint venture, and (2) an additional 1% interest in each of the two entities through which each partner owns its interest in the joint venture.

[6] During the years ended December 31, 2022 and December 31, 2020, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture that owns Dock 72 in Brooklyn, New York totaling approximately $50.7 million and $60.5 million, respectively.