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Debt and Financing Arrangements - Schedule of senior notes outstanding (Details) - USD ($) $ in Thousands | Jul. 02, 2019 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |
Carrying amount |  |  | $ 2,861,113 | $ 1,871,626
Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal amount |  |  | 2,890,000 |
Carrying amount |  |  | $ 2,861,113 | 1,871,626
Senior Notes | 7.350% senior notes due 2034 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) | [1] |  | 7.35% |
Principal amount | [1] |  | $ 300,000 |
Carrying amount |  |  | $ 297,367 | 297,254
Senior Notes | 5.144% senior notes due 2043 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) | [2] |  | 5.144% |
Principal amount | [2] |  | $ 500,000 |
Carrying amount |  |  | $ 494,944 | 494,831
Senior Notes | 4.011% senior notes due 2026 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) | [3] |  | 4.011% |
Principal amount | [3] |  | $ 500,000 |
Carrying amount |  |  | $ 497,211 | 496,806
Senior Notes | 5.031% senior notes due 2046 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) | [4] |  | 5.031% |
Principal amount |  |  | $ 450,000 |
Carrying amount |  |  | $ 445,402 | 445,317
Senior Notes | 3.635% senior notes due 2050 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) | [5] |  | 3.635% |
Principal amount |  |  | $ 1,000,000 |
Carrying amount |  |  | $ 988,500 | 0
Senior Notes | Watford notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) | [6] |  | 6.50% |
Principal amount |  |  | $ 140,000 |
Carrying amount |  |  | $ 137,689 | 137,418
Variable Interest Entity, Primary Beneficiary | Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Principal amount |  | $ 175,000 |  |
Proceeds from issuance of senior notes |  | 172,300 |  |
Variable Interest Entity, Primary Beneficiary | Senior Notes | Watford notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Stated interest rate (percentage) |  |  | 6.50% |
Watford Holdings Ltd | Variable Interest Entity, Primary Beneficiary |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Carrying amount |  |  | $ 172,689 | $ 172,418
Watford Holdings Ltd | Variable Interest Entity, Primary Beneficiary | Senior Notes |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Payments to Acquire Notes Receivable |  | $ 35,000 |  |
[1] | Senior notes of Arch Capital issued on May 4, 2004 and due May 1, 2034 (“2034 notes”).
[2] | Senior notes of Arch-U.S., a wholly-owned subsidiary of Arch Capital, issued on December 13, 2013 and due November 1, 2043 (“2043 notes”), fully and unconditionally guaranteed by Arch Capital.
[3] | Senior notes of Arch Capital Finance LLC (“Arch Finance”), a wholly-owned finance subsidiary of Arch Capital, issued on December 8, 2016 and due December 15, 2026 (“2026 notes”), fully and unconditionally guaranteed by Arch Capital.
[4] | Senior notes of Arch Finance issued on December 8, 2016 and due December 15, 2046 (“2046 notes”), fully and unconditionally guaranteed by Arch Capital
[5] | Senior notes of Arch Capital issued on June 30, 2020 and due June 30, 2050.
[6] | Senior notes of Watford issued on July 2, 2019 and due July 2, 2029, reflecting the elimination of amounts owned by Arch-U.S

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