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Unsecured Senior Notes Narrative (Details) - USD ($) $ in Thousands |  |  |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | --- | ---
Sep. 18, 2019 | Sep. 03, 2019 | Jun. 21, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  |  | $ 699,237 | $ 0
Loss from early extinguishment of debt |  |  |  |  | $ 28,010 | $ 0 | 28,010 | 0
Proceeds from unsecured senior notes |  |  |  |  |  |  | 1,548,106 | 0
Boston Properties Limited Partnership |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Repayments of Unsecured Debt |  |  |  |  |  |  | 699,237 | 0
Loss from early extinguishment of debt |  |  |  |  | 28,010 | $ 0 | 28,010 | 0
Proceeds from unsecured senior notes |  |  |  |  |  |  | 1,548,106 | $ 0
Boston Properties Limited Partnership | Senior Notes [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt, Gross |  |  |  |  | 8,450,000 |  | $ 8,450,000 |
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. |
Boston Properties Limited Partnership | Senior Notes [Member] | 10 Year Unsecured Senior Notes 3.505% [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt, Gross |  |  |  | $ 850,000 | $ 850,000 |  | $ 850,000 |
Senior Notes Pricing |  |  |  | 99.815% |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  | 3.40% | 3.40% |  | 3.40% |
Debt Instrument, Interest Rate, Effective Percentage | [1] |  |  | 3.505% | 3.505% |  | 3.505% |
Proceeds from unsecured senior notes |  |  |  | $ 841,400 |  |  |  |
Boston Properties Limited Partnership | Senior Notes [Member] | 10.5 Year Unsecured Senior Notes 2.984% [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Long-term Debt, Gross |  |  | $ 700,000 |  | $ 700,000 |  | $ 700,000 |
Senior Notes Pricing |  |  | 99.954% |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 2.90% |  | 2.90% |  | 2.90% |
Debt Instrument, Interest Rate, Effective Percentage | [1] |  | 2.984% |  | 2.984% |  | 2.984% |
Proceeds from unsecured senior notes |  |  | $ 693,800 |  |  |  |  |
Boston Properties Limited Partnership | Senior Notes [Member] | 10 Year Unsecured Senior Notes 5.708% [Member] |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 5.625% |  |  |  |  |  |
Repayments of Unsecured Debt |  | $ 740,700 |  |  |  |  |  |
Debt Instrument, Increase, Accrued Interest |  | $ 13,500 |  |  |  |  |  |
Debt Instrument, Redemption Price, Percentage |  | 103.90% |  |  |  |  |  |
Loss from early extinguishment of debt |  | $ (28,000) |  |  |  |  |  |
Redemption Premium |  | 27,300 |  |  |  |  |  |
Debt Instrument, Face Amount |  | $ 700,000 |  |  |  |  |  |
[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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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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