XML 96 R68.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Investments (Components Of Net Realized Gains, Excluding OTTI Charges) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
HTM fixed income securities gains |  |  |  |  |  |  |  |  | $ 3 | $ 5 | $ 2
HTM fixed income securities losses |  |  |  |  |  |  |  |  | (1) | (1) | (20)
Short Term Investments Realized Gains |  |  |  |  |  |  |  |  | 0 | 0 | 0
Short Term Investments Realized Losses |  |  |  |  |  |  |  |  | (13) | 0 | 0
Other investment securities gains |  |  |  |  |  |  |  |  | 3 | 162 | 1
Other investment securities losses |  |  |  |  |  |  |  |  | (4) | (653) | 0
Net realized investment gains | $ (7,686) | $ 3,688 | $ 1,765 | $ (2,704) | $ (2,600) | $ 308 | $ (3,420) | $ 18,883 | 3,562 | 31,537 | 37,703
Proceeds from sale of available-for-sale securities |  |  |  |  |  |  |  |  | 1,046,100 | 234,100 | 259,000
Fixed Income Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
AFS securities gains |  |  |  |  |  |  |  |  | 7,741 | 4,515 | 1,945
AFS securities losses |  |  |  |  |  |  |  |  | (11,411) | (312) | (392)
Equity Securities [Member] |  |  |  |  |  |  |  |  |  |  |
Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |
AFS securities gains |  |  |  |  |  |  |  |  | 8,108 | 29,168 | 36,871
AFS securities losses |  |  |  |  |  |  |  |  | $ (864) | $ (1,347) | $ (704)

X
- Definition This item represents the gross loss realized on the disposal of held-to-maturity securities during the period. + References No definition available. + Details
Name: | sigi_HeldToMaturitySecuritiesDisposedSecurityRealizedLoss
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This item represents the gross gain realized on the disposal of held-to-maturity securities during the period. + References No definition available. + Details
Name: | sigi_HeldToMaturitySecuritiesRealizedGain
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross profit realized on the sale of other investments. + References No definition available. + Details
Name: | sigi_OtherInvestmentsRealizedGains
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross loss realized on the sale of other investments. + References No definition available. + Details
Name: | sigi_OtherInvestmentsRealizedLosses
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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: | sigi_ScheduleofAvailableForSaleandHeldToMaturityLineItems
Namespace Prefix: | sigi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Gross realized gains on short term investments. + References No definition available. + Details
Name: | sigi_ShortTermInvestmentsRealizedGains
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross loss realized on the sale of short-term investments. + References No definition available. + Details
Name: | sigi_ShortTermInvestmentsRealizedLosses
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The net gain (loss) realized from the sale, exchange, redemption, or retirement of securities, not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13(h)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.3) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 + Details
Name: | us-gaap_GainLossOnSaleOfSecuritiesNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26853-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |