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Unsecured Senior Notes Unsecured Senior Notes (Narrative) (Details) - USD ($) $ in Thousands |  |  | 12 Months Ended
--- | --- | --- | ---
Dec. 17, 2017 | Dec. 04, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Debt Instrument [Line Items] |  |  |  |  |  |
Loss on Extinguishment of Debt |  |  | $ (496) |  | $ 371 | $ 22,040
Repayments of Unsecured Debt |  |  | 848,020 |  | 0 | 0
Proceeds from unsecured senior notes |  |  | $ 847,935 |  | 1,989,790 | 0
Senior Notes [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Maximum Leverage Ratio |  |  | 60.00% |  |  |
Maximum Secured Debt Leverage Ratio |  |  | 50.00% |  |  |
Minimum Interest Coverage Ratio |  |  | 1.50 |  |  |
Minimum Unencumbered Asset Value Percentage Of Unsecured Debt |  |  | 150.00% |  |  |
Boston Properties Limited Partnership |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Loss on Extinguishment of Debt |  |  | $ (496) |  | 371 | 22,040
Repayments of Unsecured Debt |  |  | 848,020 |  | 0 | 0
Proceeds from unsecured senior notes |  |  | 847,935 |  | $ 1,989,790 | $ 0
Boston Properties Limited Partnership | Senior Notes [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Long-term Debt, Gross |  |  | $ 7,300,000 |  |  |
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.35% [Member] |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Coupon/Stated Rate |  | 3.20% | 3.20% |  |  |
Senior Notes Pricing |  | 99.757% |  |  |  |
Effective Rate |  | 3.35% | 3.35% | [1] |  |
Proceeds from unsecured senior notes |  | $ 841,100 |  |  |  |
Debt Instrument, Face Amount |  | $ 850,000 |  |  |  |
Long-term Debt, Gross |  |  | $ 850,000 |  |  |
Boston Properties Limited Partnership | Senior Notes [Member] | Unsecured Senior Notes 3.853% |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt Instrument, Increase, Accrued Interest | $ 2,800 |  |  |  |  |
Debt Instrument, Redemption Price, Percentage | 101.49% |  |  |  |  |
Loss on Extinguishment of Debt | $ 13,900 |  |  |  |  |
Redemption Premium | $ 12,700 |  |  |  |  |
Coupon/Stated Rate | 3.70% |  |  |  |  |
Repayments of Unsecured Debt | $ 865,500 |  |  |  |  |
Debt Instrument, Face Amount | $ 850,000 |  |  |  |  |
[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/presentationRef -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 2: http://www.xbrl.org/2003/role/presentationRef -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://www.xbrl.org/2003/role/presentationRef -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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