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Unsecured Senior Notes (Narrative) (Details) - USD ($) $ in Thousands |  |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | --- | ---
Mar. 16, 2021 | Feb. 14, 2021 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  | $ 843,710 |  | $ 0
Loss from early extinguishment of debt |  |  | $ 0 |  | $ 0 | 898 |  | 0
Proceeds from unsecured senior notes |  |  |  |  |  | 846,345 |  | 1,248,125
Boston Properties Limited Partnership |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  | 843,710 |  | 0
Loss from early extinguishment of debt |  |  | 0 |  | $ 0 | 898 |  | 0
Proceeds from unsecured senior notes |  |  |  |  |  | $ 846,345 |  | $ 1,248,125
Debt Instrument, Covenant Description |  |  |  |  |  | The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60%, (2) a secured debt leverage ratio not to exceed 50%, (3) an interest coverage ratio of greater than 1.50, and (4) an unencumbered asset value of not less than 150% of unsecured debt. |  |
Debt Instrument, Covenant Compliance |  |  |  |  |  | At June 30, 2021, Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements. |  |
Senior Notes | Boston Properties Limited Partnership |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt |  |  | 9,700,000 |  |  | $ 9,700,000 |  |
2.671% unsecured senior notes | Senior Notes | Boston Properties Limited Partnership |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt | $ 850,000 |  | $ 850,000 |  |  | $ 850,000 |  |
Debt Instrument, Interest Rate, Stated Percentage | 2.55% |  | 2.55% |  |  | 2.55% |  |
Senior Notes Pricing | 99.57% |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 2.671% |  | 2.671% | [1] |  | 2.671% | [1] |
Proceeds from unsecured senior notes | $ 839,200 |  |  |  |  |  |  |
4.289% unsecured senior notes | Senior Notes | Boston Properties Limited Partnership |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt |  | $ 850,000 |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 4.125% |  |  |  |  |  |
Repayments of Unsecured Debt |  | $ 858,700 |  |  |  |  |  |
Debt Instrument, Increase, Accrued Interest |  | 8,700 |  |  |  |  |  |
Loss from early extinguishment of debt |  | $ 400 |  |  |  |  |  |
[1] | Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.

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