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Investments - Carrying Value of Bonds Deposited (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Schedule of Investments [Line Items] |  |
Carrying value of bonds | $ 5.6 | $ 2.8
New York |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 2.1 | 1.6
Washington |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 1.1 | 0.0
Colorado |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 1.1 | 0.0
North Carolina |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 0.3 | 0.3
New Mexico |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 0.3 | 0.3
Virginia |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 0.3 | 0.3
Nevada |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 0.2 | 0.2
Arkansas |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | 0.1 | 0.1
Massachusetts |  |
Schedule of Investments [Line Items] |  |
Carrying value of bonds | $ 0.1 | $ 0.0

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