XML 61 R49.htm IDEA: XBRL DOCUMENT
v3.19.1

Fair Value Measurements (Carrying Values and Estimated Fair Values of Financial Liabilities) (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | $ 550,104 |  |  | $ 439,540 |
Long-term debt, fair value | 594,991 |  |  | 448,622 |
Finance lease liabilities | 607 | [1] | $ 900 | 0 | [1]
Seven Point Twenty Five Percent Senior Notes [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 61,391 |  |  | 57,032 |
Seven Point Twenty Five Percent Senior Notes [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 49,907 |  |  | 49,907 |
Six Point Seventy Percent Senior Notes [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 115,671 |  |  | 107,075 |
Six Point Seventy Percent Senior Notes [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 99,467 |  |  | 99,462 |
Five Point Eight Hundred Seventy Five Senior Notes [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 0 |  |  | 177,230 |
Five Point Eight Hundred Seventy Five Senior Notes [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 0 |  |  | 185,000 |
Five Point Three Hundred Seventy Five Senior Notes [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 307,215 |  |  | 0 |
Five Point Three Hundred Seventy Five Senior Notes [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 294,097 |  |  | 0 |
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 24,474 |  |  | 24,218 |
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 25,000 |  |  | 25,000 |
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 24,426 |  |  | 24,162 |
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 25,000 |  |  | 25,000 |
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt, fair value | 61,814 |  |  | 58,905 |
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 60,000 |  |  | 60,000 |
Long Term Debt Excluding Issuance Costs and Finance Lease Obligations [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Long-term debt | 553,471 |  |  | 444,369 |
Unamortized Debt Issuance Costs [Member] | Reported Value Measurement [Member] |  |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |  |
Unamortized debt issuance costs | $ (3,974) |  |  | $ (4,829) |
[1] | Concurrent with the adoption of ASU 2016-02 discussed in Note 2. "Adoption of Accounting Pronouncements," finance lease obligations are now captured in Long-term debt on our Consolidated Balance Sheets.

X
- Definition Unamortized Debt Issuance Costs Related to Long-Term Debt + References No definition available. + Details
Name: | sigi_UnamortizedDebtIssuanceCostsRelatedtoLongTermDebt
Namespace Prefix: | sigi_
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_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Present value of lessee's discounted obligation for lease payments from finance lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918701-209980 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977 + Details
Name: | us-gaap_FinanceLeaseLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: 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(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -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 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
Name: | us-gaap_LongTermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_SevenPointTwentyFivePercentSeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_SixPointSeventyPercentSeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_FivePointEightHundredSeventyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_FivePointThreeHundredSeventyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_OnePointSixtyOnePercentBorrowingFromFederalHomeLoanBankDueJuly212021Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_OnePointFiftySixPercentBorrowingFromFederalHomeLoanBankDueAugust162021Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_ThreePointZeroThreePercentBorrowingFromFederalHomeLoanBankDueDecember162026Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_LongTermDebtExcludingIssuanceCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_UnamortizedDebtIssuanceCostsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |