Investments - Schedule of Investments Pledged as Collateral (Details) $ in Millions	Sep. 30, 2025 USD ($)
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	$ 26.8
Securities owned and pledged as collateral, fair value	118.7
U.S. government and government agencies
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	24.5
Securities owned and pledged as collateral, fair value	24.5
Obligations of states and political subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	1.8
Securities owned and pledged as collateral, fair value	1.8
RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	0.5
Securities owned and pledged as collateral, fair value	86.3
CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral on deposit with various state and regulatory agencies	0.0
Securities owned and pledged as collateral, fair value	6.1
FHLBI Collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	65.4
FHLBI Collateral \| U.S. government and government agencies
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0.0
FHLBI Collateral \| Obligations of states and political subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0.0
FHLBI Collateral \| RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	65.4
FHLBI Collateral \| CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0.0
FHLBNY Collateral
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	26.5
FHLBNY Collateral \| U.S. government and government agencies
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0.0
FHLBNY Collateral \| Obligations of states and political subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	0.0
FHLBNY Collateral \| RMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	20.4
FHLBNY Collateral \| CMBS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities pledged as collateral with FHLB	$ 6.1

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

No definition available.

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- Definition

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 825
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477351/944-825-50-1A

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- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 470
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478878/942-470-45-1

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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477734/942-470-50-3

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- Definition

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/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(11))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481444/860-30-45-1

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