Real Estate (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) ft²	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) ft²	Sep. 30, 2022 USD ($)	Sep. 26, 2023 ft²	Jul. 20, 2023 ft²	Jun. 01, 2023 ft²	Apr. 29, 2023 ft²	Jan. 30, 2023 ft²	Jan. 05, 2023 ft²
Real Estate Properties [Line Items]
Depreciation and amortization | $	$ 207,435	$ 190,675	$ 618,746	$ 551,445
Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf)	2,800,000		2,800,000
290 Binney
Real Estate Properties [Line Items]
Net Rentable Area (in sf)										566,000
Leased percentage										100.00%
300 Binney Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf)									195,000
Depreciation and amortization | $			$ 11,000
300 Binney Street | Construction in Progress
Real Estate Properties [Line Items]
Net Rentable Area (in sf)									236,000
Leased percentage									100.00%
2100 Pennsylvania Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf)								476,000
View Boston
Real Estate Properties [Line Items]
Net Rentable Area (in sf)							63,000
140 Kendrick Street - Building A
Real Estate Properties [Line Items]
Net Rentable Area (in sf)						104,000
180 CityPoint [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf)					329,000