XML 93 R66.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Investments (Investments Pledged as Collateral) (Details) $ in Millions | Dec. 31, 2015 USD ($)
--- | ---
Schedule of Available-for-sale Securities [Line Items] |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | $ 63.7
Securities Pledged As Collateral For Reinsurance Obligations | 11.5
Assets Held by Insurance Regulators | 24.0
Securities pledged as collateral for reinsurance obligations | 99.2
Outstanding borrowing with the Federal Home Loan Bank of Indianapolis | 60.0
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 | 7.5
Securities Pledged As Collateral For Reinsurance Obligations | 0.0
Assets Held by Insurance Regulators | 24.0
Securities pledged as collateral for reinsurance obligations | 31.5
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 | 0.0
Securities Pledged As Collateral For Reinsurance Obligations | 5.0
Assets Held by Insurance Regulators | 0.0
Securities pledged as collateral for reinsurance obligations | 5.0
Corporate Securities [Member] |
Schedule of Available-for-sale Securities [Line Items] |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | 0.0
Securities Pledged As Collateral For Reinsurance Obligations | 4.7
Assets Held by Insurance Regulators | 0.0
Securities pledged as collateral for reinsurance obligations | 4.7
Commercial Mortgage Backed Securities [Member] |
Schedule of Available-for-sale Securities [Line Items] |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | 1.2
Securities Pledged As Collateral For Reinsurance Obligations | 0.0
Assets Held by Insurance Regulators | 0.0
Securities pledged as collateral for reinsurance obligations | 1.2
Residential Mortgage Backed Securities [Member] |
Schedule of Available-for-sale Securities [Line Items] |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | 55.0
Securities Pledged As Collateral For Reinsurance Obligations | 1.8
Assets Held by Insurance Regulators | 0.0
Securities pledged as collateral for reinsurance obligations | $ 56.8

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 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64702-112823 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 FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesLongTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6467456&loc=d3e113888-111728 + Details
Name: | us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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