Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	$ 66.3	$ 64.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.9	2.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.1	0.0
Debt Securities, Available-for-sale, Restricted	67.1	66.1
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	33.2	31.3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.4	1.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.1	0.0
Debt Securities, Available-for-sale, Restricted	33.5	32.4
US Government and Agency Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	19.8	19.7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.4	0.7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Restricted	20.2	20.4
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	12.9	12.7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.1	0.2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0
Debt Securities, Available-for-sale, Restricted	13.0	12.9
Mortgage-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	0.4	0.4
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	$ 0.4	$ 0.4

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 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

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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-Publisher FASB
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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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