The cash inflow from the bond proceeds contributed to the Insurance Subsidiaries as capital.

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The amount of debt discount that was originally recognized at the issuance of the instrument.

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Remaining proceeds from the issuance of debt, net of issuance costs and after the redemption of previous debt outstanding.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of Federal Home Loan Bank (FHLBank) advances to member financial institutions.

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Interest rate of advances made and reported by Federal Home Loan Bank (FHLBank).

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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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The effective interest rate at the end of the reporting period.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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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.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Indebtedness (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Indebtedness (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2005	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2004
Maximum borrowing percentage		10.00%
Borrowing threshold of FHLBI		20
Debt Issuance Costs, Gross		$ 3,300
Long-term debt		550,743	$ 550,597
Selective Insurance Group [Member]
Line of Credit, Current		$ 50,000
Line of Credit Facility, Interest Rate at Period End		2.244%
Five Point Three Hundred Seventy Five [Member]
Long-term Debt, Gross		$ 300,000
Interest Rate		5.375%
Discount for notes issued		$ 5,900
Net proceeds from the issuance		290,800
Five Point Eight Hundred Seventy Five Percent Senior Notes [Member]
Long-term Debt, Gross		$ 185,000
Interest Rate		5.875%
Debt Retirement Costs Before Tax		$ 4,200
Debt Retirement Costs Net of Tax		3,300
Proceeds From Debt Issuance After Redemption		106,000
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Long-term Debt, Gross		$ 60,000
Interest Rate		3.03%
Federal Home Loan Bank Advances			45,000
Net proceeds from the issuance			15,000
Six Point Seventy Percent Senior Notes due 2035 [Member]
Long-term Debt, Gross		$ 100,000
Interest Rate		6.70%
Acceleration of principal		$ 10,000
Discount for notes issued	$ 700
Effective yield	6.754%
Net proceeds from the issuance	$ 50,000
Seven Point Twenty Five Percent Senior Notes due 2034 [Member]
Long-term Debt, Gross		$ 50,000
Interest Rate		7.25%
Acceleration of principal		$ 10,000
Discount for notes issued				$ 100
Effective yield				7.27%
Bond proceeds to Insurance Subsidiaries as capital				$ 25,000
Line of Credit expires Dec.20, 2022 [Member]
Line of credit borrowing capacity		50,000	30,000
Line of credit, maximum borrowing capacity		125,000	50,000
Acceleration of principal		$ 20,000
Maximum borrowing percentage		10.00%
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Long-term Debt, Gross		$ 25,000
Interest Rate		1.61%
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Long-term Debt, Gross		$ 25,000
Interest Rate		1.56%
Zero Point Seventy Eight Percent Borrowing from FHLBNY Due September 14, 2020. [Member]
Federal Home Loan Bank Advances		$ 100,000
Zero Point Seventy Eight Percent Borrowing from FHLBNY Due September 14, 2020. [Member] \| Selective Insurace Company of America (SICA) [Member]
Federal Home Loan Bank, Advances, Interest Rate		0.78%
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member] \| Selective Insurace Company of America (SICA) [Member]
Federal Home Loan Bank, Advances, Interest Rate		0.36%
Zero Point Sixty Eight Percent Borrowing from FHLBNY Due September 18, 2020 [Member] \| Selective Insurace Company of America (SICA) [Member]
Federal Home Loan Bank, Advances, Interest Rate		0.68%
Zero Point Thirty Three Percent Borrowing from FHLBNY Due December 16, 2020 [Member] \| Selective Insurace Company of America (SICA) [Member]
Federal Home Loan Bank, Advances, Interest Rate		0.33%
One Point Eighty One Percent Borrowing From Federal Home Loan Bank Due February 18, 2020 [Member]
Federal Home Loan Bank Advances		$ 85,000
Federal Home Loan Bank, Advances, Interest Rate		1.81%
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member] \| Selective Insurance Company of South Carolina (SICSC) [Member]
Federal Home Loan Bank Advances		$ 39,000
Federal Home Loan Bank, Advances, Interest Rate		0.58%
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member] \| Selective Insurance Company of the Southeast (SICSE) [Member]
Federal Home Loan Bank Advances		$ 28,000
Federal Home Loan Bank, Advances, Interest Rate		0.58%
Federal Home Loan Bank of Indianapolis [Member]
Aggregate investment in FHLBI		$ 5,700	$ 2,800
Federal Home Loan Bank of New York [Member]
Aggregate investment in FHLBI		$ 3,100