Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	$ 101.5	$ 94.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.1	0.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1.7	2.0
Debt Securities, Available-for-sale, Restricted	99.9	93.2
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	44.7	40.5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.7	0.9
Debt Securities, Available-for-sale, Restricted	44.0	39.9
US Government and Agency Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	35.1	35.2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.8	0.9
Debt Securities, Available-for-sale, Restricted	34.3	34.5
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	20.8	18.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.1	0.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.2	0.2
Debt Securities, Available-for-sale, Restricted	20.7	17.9
Municipal Bonds
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	0.8	0.7
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	0.8	0.7
Mortgage-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	0.1	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	$ 0.1	$ 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
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
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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
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
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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.

+ References

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