XML 65 R53.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Reserve for Loss and Loss Expense (Rollforward of Reserve for Loss and Loss Expense) (Details) - USD ($) $ in Thousands | 9 Months Ended
--- | ---
Sep. 30, 2018 | Sep. 30, 2017
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Increase in current year loss and loss expense incurred | $ 111,000 |
Increase in non catastrophe property losses | 61,900 |
Non catastrophe property losses | 278,500 |
Gross reserve for loss and loss expense, at beginning of year | 3,771,240 | $ 3,691,719
Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year | 585,855 | 611,200
Net reserve for loss and loss expense, at beginning of year | 3,185,385 | 3,080,519
Incurred loss and loss expense for claims occurring in the current year | 1,148,032 | 1,037,079
Total incurred loss and loss expense | 1,130,468 | 1,003,618
Paid loss and loss expense for claims occurring in the current year | 369,036 | 314,686
Paid loss and loss expense for claims occurring in the prior years | 610,734 | 581,186
Total paid loss and loss expense | 979,770 | 895,872
Net reserve for loss and loss expense, at end of period | 3,336,083 | 3,188,265
Add: reinsurance recoverable on unpaid loss and loss expense, at end of period | 589,072 | 647,535
Gross reserve for loss and loss expense, at end of period | 3,925,155 | 3,835,800
Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | (17,564) | (33,461)
Property Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | 6,400 |
Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | (24,000) |
General Liability [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | (8,000) | (48,300)
Excess And Surplus Operations [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | 12,000 | 10,000
Personal Automobile [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development |  | 4,000
Commercial Automobile [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | 25,000 | 26,000
Workers Compensation [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development | $ (53,000) | $ (29,300)

X
- Definition Increase decrease in non catastrophe property losses + References No definition available. + Details
Name: | sigi_Increasedecreaseinnoncatastrophepropertylosses
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Property losses resulting from events other than catastrophes. + References No definition available. + Details
Name: | sigi_NonCatastrophePropertyLosses
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
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_LiabilityForClaimsAndClaimsAdjustmentExpenseLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in the current period and related claims settlement costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in prior periods and related claims settlement costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(13)(a)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount, after effects of reinsurance, of increase (decrease) in the liability for unpaid claims and claims adjustment expense. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpensePeriodIncreaseDecrease
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585 + Details
Name: | us-gaap_PaymentsForLossesAndLossAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=99382578&loc=d3e14764-158437 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis=sigi_ChangeinHistoricalClaimRateExperienceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_PropertyInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=sigi_CasualtyInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_GeneralLiabilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_ExcessAndSurplusOperationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_PersonalAutomobileMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_CommercialAutomobileMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_WorkersCompensationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |