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Real Estate (Narrative) (Details) $ in Thousands |  |  |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 25, 2020 USD ($) ft² | Feb. 20, 2020 USD ($) ft² Buildings | Jan. 28, 2020 USD ($) ft² Buildings | Jan. 27, 2020 USD ($) | Feb. 19, 2020 USD ($) | Jun. 30, 2020 USD ($) | Jun. 24, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) | Jun. 24, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 26, 2020 USD ($) ft² | Jun. 01, 2020 ft² | Mar. 26, 2020 ft²
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales of real estate |  |  |  |  |  |  |  |  |  | $ 506,337 |  |  | $ 60,398 |  |  |
Gains on sales of real estate |  |  |  |  |  | $ 203,767 |  |  | $ 1,686 | 613,932 |  |  | 781 |  |  |
Payments to Acquire Equity Method Investments |  |  |  |  |  |  |  |  |  | 106,168 |  |  | 50,068 |  |  |
Revenues |  |  |  |  |  | $ 654,773 |  |  | 733,741 | $ 1,407,329 |  |  | 1,459,508 |  |  |
Capital Gallery [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² | 455,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contractual Sales Price | $ 253,700 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales of real estate | 246,900 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on sales of real estate | $ 203,800 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Income (Loss) |  |  |  |  |  |  |  | $ 2,900 | 3,500 |  |  | $ 6,300 | 7,000 |  |  |
New Dominion Technology Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  | 493,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contractual Sales Price |  | $ 256,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales of real estate |  | 254,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on sales of real estate |  | $ 192,300 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Income (Loss) |  |  |  |  | $ 1,600 |  |  |  | 2,100 |  |  |  | 4,200 |  |  |
number of buildings | Buildings |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gateway Center [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on sales of real estate |  |  | $ 217,700 |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Income (Loss) |  |  |  | $ 200 |  |  |  |  | 3,100 |  |  |  | 6,000 |  |  |
425 Fourth Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 140,100 |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  | 804,000 |  |
17Fifty Presidents Street [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 276,000
Leased percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00%
20 Citypoint [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 211,000 |
Leased percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 62.00% |
Capital Gallery [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² | 631,000 |  |  |  |  |  |  |  |  |  |  |  |  | 176,000 |  |
Gateway Commons Complex [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  | 768,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  | $ 350,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  | 50.00% |  |  | 50.00% | [1] |  |  | 50.00% | [1] |  |  |  |  |
number of buildings | Buildings |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |
Gateway Commons Complex prior to deferred contribution [Member] [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  | 55.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Gateway Commons Complex Future Development[Member] [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  | 49.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Joint Venture Partner [Member] | Gateway Commons Complex [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net Rentable Area (in sf) | ft² |  |  | 768,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Equity Method Investments |  |  | $ 280,800 |  |  |  |  |  |  |  |  |  |  |  |  |
Future payment to acquire interest in equity method investment |  |  | $ 69,200 |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |
number of buildings | Buildings |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |
Joint Venture Partner [Member] | Gateway Commons Complex Future Development[Member] [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership Percentage |  |  | 51.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Boston Properties Limited Partnership |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales of real estate |  |  |  |  |  |  |  |  |  | $ 506,337 |  |  | 60,398 |  |  |
Gains on sales of real estate |  |  |  |  |  | $ 207,241 |  |  | 1,835 | 626,895 |  |  | 930 |  |  |
Payments to Acquire Equity Method Investments |  |  |  |  |  |  |  |  |  | 106,168 |  |  | 50,068 |  |  |
Revenues |  |  |  |  |  | $ 654,773 |  |  | $ 733,741 | $ 1,407,329 |  |  | $ 1,459,508 |  |  |
Boston Properties Limited Partnership | Capital Gallery [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on sales of real estate | $ 207,200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Boston Properties Limited Partnership | New Dominion Technology Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on sales of real estate |  | $ 197,100 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Boston Properties Limited Partnership | Gateway Center [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gains on sales of real estate |  |  | $ 222,400 |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | As a result of the partner’s deferred contribution, the Company owns an approximately 55% interest in the joint venture at June 30, 2020. Future development projects will be owned 49% by the Company and 51% by its partner.

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