Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	$ 90.0	$ 76.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	3.8	3.8
Debt Securities, Available-for-sale, Restricted	86.2	72.3
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	37.8	32.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1.6	1.7
Debt Securities, Available-for-sale, Restricted	36.2	30.9
US Government and Agency Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	34.3	29.5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1.7	1.7
Debt Securities, Available-for-sale, Restricted	32.6	27.8
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	16.9	13.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.5	0.4
Debt Securities, Available-for-sale, Restricted	16.4	13.4
Municipal Bonds
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	0.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0
Debt Securities, Available-for-sale, Restricted	0.8
Mortgage-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	0.2	0.2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Restricted	$ 0.2	$ 0.2

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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