XML 95 R85.htm IDEA: XBRL DOCUMENT
v3.23.2

Fair Values of Assets and Liabilities - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands | Jun. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | $ 109,896 |  | $ 106,100
U.S. Government-sponsored enterprises obligations [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 1,840 |  | 1,826
U.S. Government agency small business administration pools guaranteed by SBA [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 7,788 | [1] | 8,359
Collateralized mortgage obligations issued by the FHLMC, FNMA and GNMA [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 5,864 | [1] | 6,222
Residential mortgage backed securities [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 21,672 | [1] | 21,823
Municipal bonds [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 65,141 |  | 62,416
Corporate debt [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 485 |  | 497
Corporate subordinated debt [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 7,106 |  | 4,957
Fair Value, Measurements, Recurring [Member] | U.S. Government-sponsored enterprises obligations [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 1,840 |  | 1,826
Fair Value, Measurements, Recurring [Member] | U.S. Government agency small business administration pools guaranteed by SBA [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 7,788 |  | 8,359
Fair Value, Measurements, Recurring [Member] | Collateralized mortgage obligations issued by the FHLMC, FNMA and GNMA [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 5,864 |  | 6,222
Fair Value, Measurements, Recurring [Member] | Residential mortgage backed securities [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 21,672 |  | 21,823
Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 65,141 |  | 62,416
Fair Value, Measurements, Recurring [Member] | Corporate debt [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 485 |  | 497
Fair Value, Measurements, Recurring [Member] | Corporate subordinated debt [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 7,106 |  | 4,957
Fair Value, Measurements, Recurring [Member] | Derivative [Member] |  |  |
Other assets: |  |  |
Other assets, at fair value | 326 |  | 961
Other liabilities: |  |  |
Other liabilities, at fair value | 48 |  |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government-sponsored enterprises obligations [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 1,840 |  | 1,826
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government agency small business administration pools guaranteed by SBA [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 7,788 |  | 8,359
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized mortgage obligations issued by the FHLMC, FNMA and GNMA [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 5,864 |  | 6,222
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential mortgage backed securities [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 21,672 |  | 21,823
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 65,141 |  | 62,416
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate debt [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 485 |  | 497
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate subordinated debt [Member] |  |  |
Securities available-for-sale: |  |  |
Securities available-for-sale, at fair value | 7,106 |  | 4,957
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member] |  |  |
Other assets: |  |  |
Other assets, at fair value | 326 |  | 961
Other liabilities: |  |  |
Other liabilities, at fair value | 48 |  |
Fair Value, Measurements, Recurring [Member] | Mortgage servicing rights [Member] |  |  |
Other assets: |  |  |
Other assets, at fair value | 350 |  | 357
Fair Value, Measurements, Recurring [Member] | Mortgage servicing rights [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |
Other assets: |  |  |
Other assets, at fair value | $ 350 |  | $ 357
[1] | Actual maturities for these debt securities are dependent upon the interest rate environment and prepayments on the underlying loans.

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount 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 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (aa) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481830/320-10-45-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479130/326-30-45-1 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_LiabilitiesFairValueDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedMortgageObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_MunicipalBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=fsea_CorporateSubordinatedDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_DerivativeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=fsea_MortgageServicingRightsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |