XML 130 R66.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Investments (Investments Pledged as Collateral) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Sep. 30, 2014
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  | $ 60.7 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Outstanding borrowing with the Federal Home Loan Bank of Indianapolis | 45 us-gaap_FederalHomeLoanBankAdvancesLongTerm |
Securities pledged as collateral for reinsurance obligations |  | 100.4 sigi_SecuritiesPledgedAsCollateral
Securities Pledged As Collateral For Reinsurance Obligations |  | 14.4 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations
Assets Held by Insurance Regulators |  | 25.3 us-gaap_AssetsHeldByInsuranceRegulators
U.S. Government and Government Agencies [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | 7.7 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / invest_InvestmentSectorAxis = us-gaap_USTreasuryAndGovernmentMember |
Securities pledged as collateral for reinsurance obligations | 33.0 sigi_SecuritiesPledgedAsCollateral / invest_InvestmentSectorAxis = us-gaap_USTreasuryAndGovernmentMember |
Securities Pledged As Collateral For Reinsurance Obligations | 0 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations / invest_InvestmentSectorAxis = us-gaap_USTreasuryAndGovernmentMember |
Assets Held by Insurance Regulators | 25.3 us-gaap_AssetsHeldByInsuranceRegulators / invest_InvestmentSectorAxis = us-gaap_USTreasuryAndGovernmentMember |
Obligations of States and Political Subdivisions [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  | 0 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / invest_InvestmentSectorAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Securities pledged as collateral for reinsurance obligations |  | 5.7 sigi_SecuritiesPledgedAsCollateral / invest_InvestmentSectorAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Securities Pledged As Collateral For Reinsurance Obligations |  | 5.7 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations / invest_InvestmentSectorAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Assets Held by Insurance Regulators |  | 0 us-gaap_AssetsHeldByInsuranceRegulators / invest_InvestmentSectorAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Corporate Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  | 0 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / invest_InvestmentSectorAxis = us-gaap_CorporateDebtSecuritiesMember
Securities pledged as collateral for reinsurance obligations |  | 5.3 sigi_SecuritiesPledgedAsCollateral / invest_InvestmentSectorAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Pledged As Collateral For Reinsurance Obligations |  | 5.3 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations / invest_InvestmentSectorAxis = us-gaap_CorporateDebtSecuritiesMember
Assets Held by Insurance Regulators |  | 0 us-gaap_AssetsHeldByInsuranceRegulators / invest_InvestmentSectorAxis = us-gaap_CorporateDebtSecuritiesMember
Asset-backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  | 0 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / invest_InvestmentSectorAxis = us-gaap_AssetBackedSecuritiesMember
Securities pledged as collateral for reinsurance obligations |  | 1.1 sigi_SecuritiesPledgedAsCollateral / invest_InvestmentSectorAxis = us-gaap_AssetBackedSecuritiesMember
Securities Pledged As Collateral For Reinsurance Obligations |  | 1.1 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations / invest_InvestmentSectorAxis = us-gaap_AssetBackedSecuritiesMember
Assets Held by Insurance Regulators |  | 0 us-gaap_AssetsHeldByInsuranceRegulators / invest_InvestmentSectorAxis = us-gaap_AssetBackedSecuritiesMember
Commercial Mortgage Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  | 2.2 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / invest_InvestmentSectorAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Securities pledged as collateral for reinsurance obligations |  | 2.2 sigi_SecuritiesPledgedAsCollateral / invest_InvestmentSectorAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Securities Pledged As Collateral For Reinsurance Obligations |  | 0 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations / invest_InvestmentSectorAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Assets Held by Insurance Regulators |  | 0 us-gaap_AssetsHeldByInsuranceRegulators / invest_InvestmentSectorAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Residential Mortgage Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged |  | 50.8 us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1 / invest_InvestmentSectorAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Securities pledged as collateral for reinsurance obligations |  | 53.1 sigi_SecuritiesPledgedAsCollateral / invest_InvestmentSectorAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Securities Pledged As Collateral For Reinsurance Obligations |  | 2.3 sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations / invest_InvestmentSectorAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Assets Held by Insurance Regulators |  | $ 0 us-gaap_AssetsHeldByInsuranceRegulators / invest_InvestmentSectorAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember

X
- Definition Total value amount of investments pledged as collateral + References No definition available. + Details
Name: | sigi_SecuritiesPledgedAsCollateral
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The carrying value of investments pledged as collateral for reinsurance obligations + References No definition available. + Details
Name: | sigi_SecuritiesPledgedAsCollateralForReinsuranceObligations
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 320 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=28366721&loc=d3e22002-158495 + Details
Name: | us-gaap_AssetsHeldByInsuranceRegulators
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of the collateral pledged in support of federal home loan bank advances outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64702-112823 + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesLongTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | invest_InvestmentSectorAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSectorAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | invest_InvestmentSectorAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentSectorAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |