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Real Estate (Narrative) (Details) $ in Thousands |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |
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Dec. 14, 2023 USD ($) ft² a buildings | Dec. 31, 2023 USD ($) ft² Real_Estate_Properties | Dec. 31, 2023 USD ($) ft² Real_Estate_Properties | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 13, 2023 USD ($) | Nov. 30, 2023 ft² | Nov. 13, 2023 | Oct. 05, 2023 ft² | 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] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  | $ 3,273,569 | $ 3,108,581 | $ 2,888,621 |  |  |  |  |  |  |  |  |  |
Net Income (Loss) Attributable to Parent |  |  |  | 190,215 | 848,947 | 505,195 |  |  |  |  |  |  |  |  |  |
Depreciation and amortization |  |  |  | 830,813 | 749,775 | $ 717,336 |  |  |  |  |  |  |  |  |  |
Carying value of the Company's investment in unconsolidated joint ventures |  |  | $ 1,377,319 | $ 1,377,319 | $ 1,715,911 |  |  |  |  |  |  |  |  |  |  |
Santa Monica Business Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage | [1] |  |  |  | 55.00% |  |  |  |  |  |  |  |  |  |  |
Carying value of the Company's investment in unconsolidated joint ventures | [2] |  |  |  | $ 164,735 |  |  |  |  |  |  |  |  |  |  |
Joint Venture Partner [Member] | Santa Monica Business Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  | 45.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction in Progress |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  | 2,700,000 | 2,700,000 |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate properties | Real_Estate_Properties |  |  | 10 | 10 |  |  |  |  |  |  |  |  |  |  |  |
Santa Monica Business Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Land Subject to Ground Leases | a |  | 47 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  | 1,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate properties | buildings |  | 21 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lessee, Finance Lease, Remaining Lease Term |  | 75 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Investments |  | $ 38,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Working Capital, Including Cash Acquired from Acquisition |  | 20,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale / consolidation |  | $ 29,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  | $ 3,900 |  |  |  |  |  |  |  |  |  |  |  |  |
Net Income (Loss) Attributable to Parent |  |  | $ (900) |  |  |  |  |  |  |  |  |  |  |  |  |
Land subject to ground lease, percentage |  | 70.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Santa Monica Business Park [Member] | Santa Monica Business Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale / consolidation |  | $ 29,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Santa Monica Business Park [Member] | Mortgages [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Santa Monica Business Park [Member] | Company's Share [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Carying value of the Company's investment in unconsolidated joint ventures |  |  |  |  |  |  | $ 149,900 |  |  |  |  |  |  |  |  |
290 Binney | Construction in Progress |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 566,000
Leased percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00%
300 Binney Street |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 195,000 |
Depreciation and amortization |  |  |  | $ 11,000 |  |  |  |  |  |  |  |  |  |  |  |
300 Binney Street | Noncontrolling Interest [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners |  |  |  |  |  |  |  |  | 45.00% |  |  |  |  |  |  |
300 Binney Street | Construction in Progress |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 236,000 |
Leased percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |
2100 Pennsylvania Avenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  | 476,000 |  |
View Boston |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  | 63,000 |  |  |
140 Kendrick Street - Building A |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  | 104,000 |  |  |  |
180 CityPoint [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  | 329,000 |  |  |  |  |
103 CityPoint |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  | 113,000 |  |  |  |  |  |
105 Carnegie Center |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  | 70,000 |  |  |  |  |  |  |  |
105 Carnegie Center | Future construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  | 73,000 |  |  |  |  |  |  |  |
[1] | During the year ended December 31, 2023, the Company completed the acquisition of its joint venture partner’s 45% ownership interest in Santa Monica Business Park, as described below in this Note 6 and Note 3.
[2] | Investments with deficit balances aggregating approximately $39.9 million and $85.4 million at December 31, 2023 and December 31, 2022, respectively, are included within Other Liabilities in the Company’s Consolidated Balance Sheets.

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