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Retirement Plans (Tables) | 12 Months Ended
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Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Plan Terms In Effect And Revisions Of Retirement Savings Plan | (a) Selective Insurance Retirement Savings Plan (“Retirement Savings Plan”) SICA offers a voluntary defined contribution 401(k) plan, which is available to most of our employees and is a tax-qualified retirement plan subject to the Employee Retirement Income Security Act of 1974 ("ERISA"). Expense recorded for this plan was $15.0 million in 2016, $14.1 million in 2015, and $13.4 million in 2014.
Schedule of Funded Status Of Retirement Income Plan And Retirement Life Plan |
December 31, |  | Pension Plan
($ in thousands) |  | 2016 |  | 2015
Change in Benefit Obligation: |  |  |  |  |  |
Benefit obligation, beginning of year |  | $ | 310,308 |  |  | 322,271 |
Service cost |  | 1,647 |  |  | 7,215 |
Interest cost |  | 12,336 |  |  | 13,668 |
Actuarial losses (gains) |  | 15,086 |  |  | (24,994 | )
Benefits paid |  | (8,789 | ) |  | (7,852 | )
Benefit obligation, end of year |  | $ | 330,588 |  |  | 310,308 |
Change in Fair Value of Assets: |  |  |  |  |  |
Fair value of assets, beginning of year |  | $ | 249,700 |  |  | 253,452 |
Actual return on plan assets, net of expenses |  | 21,079 |  |  | (7,600 | )
Contributions by the employer to funded plans |  | 54,525 |  |  | 11,700 |
Benefits paid |  | (8,789 | ) |  | (7,852 | )
Fair value of assets, end of year |  | $ | 316,515 |  |  | 249,700 |
Funded status |  | $ | (14,073 | ) |  | (60,608 | )
Schedule of Amounts Recognized in Consolidated Balance Sheet |
Amounts Recognized in the Consolidated Balance Sheet: |  |  |  |  |  |
Liabilities |  | $ | (14,073 | ) |  | (60,608 | )
Net pension liability, end of year |  | $ | (14,073 | ) |  | (60,608 | )
Schedule of Amounts recognized in Accumulated Other than Comprehensive Income |
Amounts Recognized in AOCI: |  |  |  |  |  |
Net actuarial loss |  | $ | 85,845 |  |  | 80,828 |
Total |  | $ | 85,845 |  |  | 80,828 |
Schedule of Other Information as of December 31 |
Other Information as of December 31: |  |  |  |  |  |
Accumulated benefit obligation |  | $ | 330,588 |  |  | 310,307 |
Schedule of Components Of Net Periodic Benefit Cost And Other Amounts Recognized In Other Comprehensive Income |
|  | Pension Plan
($ in thousands) |  | 2016 |  | 2015 |  | 2014
Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Income: |  |  |  |  |  |  |  |  |
Net Periodic Benefit Cost: |  |  |  |  |  |  |  |  |
Service cost |  | $ | 1,647 |  |  | 7,215 |  |  | 5,763 |
Interest cost |  | 12,336 |  |  | 13,668 |  |  | 12,776 |
Expected return on plan assets |  | (17,309 | ) |  | (15,969 | ) |  | (15,671 | )
Amortization of unrecognized actuarial loss |  | 6,299 |  |  | 6,831 |  |  | 1,776 |
Total net periodic cost |  | $ | 2,973 |  |  | 11,745 |  |  | 4,644 |
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income: |  |  |  |  |  |  |  |  |
Net actuarial loss (gain) |  | $ | 11,316 |  |  | (1,425 | ) |  | 52,556 |
Reversal of amortization of net actuarial loss |  | (6,299 | ) |  | (6,831 | ) |  | (1,776 | )
Total recognized in other comprehensive income |  | $ | 5,017 |  |  | (8,256 | ) |  | 50,780 |
Total recognized in net periodic benefit cost and other comprehensive income |  | $ | 7,990 |  |  | 3,489 |  |  | 55,424 |
Schedule Of Weighted- Average Expense and Liability Assumptions |
Weighted-Average Liability Assumptions as of December 31: |  |  |  |  |
Discount rate |  | 4.41 | % |  | 4.69
Rate of compensation increase |  | — |  |  | 4.00
|  | Pension Plan
|  | 2016 |  | 2015 |  | 2014
Weighted-Average Expense Assumptions for the years ended December 31: |  |  |  |  |  |  |
Discount rate |  | 4.69 | % |  | 4.29 |  | 5.16
Expected return on plan assets |  | 6.37 |  |  | 6.27 |  | 6.92
Rate of compensation increase 1 |  | — |  |  | 4.00 |  | 4.00
Schedule of Allocation of Plan Assets |
|  | 2016 |  | 2015
|  | Target Ranges |  | Actual Percentage |  | Actual Percentage
Long duration fixed income |  | 40%-100% |  |  | 53 | % |  | 60 | %
Global equity |  | 0%-40% |  |  | 33 | % |  | 36 | %
Alternatives & other return seeking assets 1 |  | 0%-30% |  |  | 6 | % |  | 3 | %
Cash and short-term investments |  | 0%-5% |  |  | 8 | % |  | 1 | %
Total |  | — | % |  | 100 | % |  | 100 | %
Schedule of Quantitative Disclosures of our Financial Assets that were Measured at Fair Value |
December 31, 2016 |  |  |  | Fair Value Measurements Using
($ in thousands) |  | Assets Measured at Fair Value 12/31/16 |  | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)1 |  | Significant Other Observable Inputs (Level 2)1 |  | Significant Unobservable Inputs (Level 3)
Description |  |  |  |  |  |  |  |  |  |  |  |
Measured on a recurring basis: |  |  |  |  |  |  |  |  |  |  |  |
AFS fixed income securities: |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 77,333 |  |  | 27,520 |  |  | 49,813 |  |  | — |
Foreign government |  | 26,865 |  |  | — |  |  | 26,865 |  |  | — |
Obligations of states and political subdivisions |  | 1,379,593 |  |  | — |  |  | 1,379,593 |  |  | — |
Corporate securities |  | 1,997,753 |  |  | — |  |  | 1,997,753 |  |  | — |
CLO and other ABS |  | 528,960 |  |  | — |  |  | 528,960 |  |  | — |
CMBS |  | 256,842 |  |  | — |  |  | 256,842 |  |  | — |
RMBS |  | 525,194 |  |  | — |  |  | 525,194 |  |  | — |
Total AFS fixed income securities |  | 4,792,540 |  |  | 27,520 |  |  | 4,765,020 |  |  | — |
AFS equity securities: |  |  |  |  |  |  |  |
Common stock |  | 130,608 |  |  | 122,932 |  |  | — |  |  | 7,676 |
Preferred stock |  | 16,145 |  |  | 16,145 |  |  | — |  |  | — |
Total AFS equity securities |  | 146,753 |  |  | 139,077 |  |  | — |  |  | 7,676 |
Total AFS securities |  | 4,939,293 |  |  | 166,597 |  |  | 4,765,020 |  |  | 7,676 |
Short-term investments |  | 221,701 |  |  | 221,701 |  |  | — |  |  | — |
Total assets measured at fair value |  | $ | 5,160,994 |  |  | 388,298 |  |  | 4,765,020 |  |  | 7,676 |
December 31, 2015 |  |  |  | Fair Value Measurements Using
($ in thousands) |  | Assets Measured at Fair Value 12/31/15 |  | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1)1 |  | Significant Other Observable Inputs (Level 2)1 |  | Significant Unobservable Inputs (Level 3)
Description |  |  |  |  |  |  |  |  |  |  |  |
Measured on a recurring basis: |  |  |  |  |  |  |  |  |  |  |  |
AFS fixed income securities: |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 104,115 |  |  | 42,702 |  |  | 61,413 |  |  | — |
Foreign government |  | 15,181 |  |  | — |  |  | 15,181 |  |  | — |
Obligations of states and political subdivisions |  | 1,359,142 |  |  | — |  |  | 1,359,142 |  |  | — |
Corporate securities |  | 1,900,182 |  |  | — |  |  | 1,900,182 |  |  | — |
CLO and other ABS |  | 244,154 |  |  | — |  |  | 244,154 |  |  | — |
CMBS |  | 243,592 |  |  | — |  |  | 243,592 |  |  | — |
RMBS |  | 541,837 |  |  | — |  |  | 541,837 |  |  | — |
Total AFS fixed income securities |  | 4,408,203 |  |  | 42,702 |  |  | 4,365,501 |  |  | — |
AFS equity securities: |  |  |  |  |  |  |  |
Common stock |  | 194,789 |  |  | 191,517 |  |  | — |  |  | 3,272 |
Preferred stock |  | 12,262 |  |  | 12,262 |  |  | — |  |  | — |
Total AFS equity securities |  | 207,051 |  |  | 203,779 |  |  | — |  |  | 3,272 |
Total AFS securities |  | 4,615,254 |  |  | 246,481 |  |  | 4,365,501 |  |  | 3,272 |
Short-term investments |  | 194,819 |  |  | 194,819 |  |  | — |  |  | — |
Total assets measured at fair value |  | $ | 4,810,073 |  |  | 441,300 |  |  | 4,365,501 |  |  | 3,272 |
1 There were no transfers of securities between Level 1 and Level 2.
Schedule of Expected Benefit Payments | Payments
($ in thousands) |  | Pension Plan
Benefits Expected to be Paid in Future |  |  |
Fiscal Years: |  |  |
2017 |  | $ | 10,830 |
2018 |  | 12,041 |
2019 |  | 13,125 |
2020 |  | 14,184 |
2021 |  | 15,124 |
2022-2026 |  | 89,771 |
Retirement Income Plan [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule of Quantitative Disclosures of our Financial Assets that were Measured at Fair Value |
December 31, 2016 |  |  |  | Fair Value Measurements at 12/31/16 Using
($ in thousands) |  | Assets Measured at Fair Value At 12/31/16 |  | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) |  | Significant Other Observable Inputs (Level 2) |  | Significant Unobservable Inputs (Level 3)
Description |  |  |  |  |  |  |  |  |  |  |  |
Long-duration fixed income: |  |  |  |  |  |  |  |  |  |  |  |
Global asset allocation fund |  | $ | 37,878 |  |  | 37,878 |  |  | — |  |  | — |
Extended duration fixed income |  | 131,457 |  |  | 131,457 |  |  | — |  |  | — |
Total long duration fixed income |  | 169,335 |  |  | 169,335 |  |  | — |  |  | — |
Cash and short-term investments: |  |  |  |  |  |  |  |
Short-term investments |  | 23,722 |  |  | 23,722 |  |  | — |  |  | — |
Deposit administration contracts |  | 1,832 |  |  | — |  |  | 1,832 |  |  | — |
Total cash and short-term investments |  | 25,554 |  |  | 23,722 |  |  | 1,832 |  |  | — |
Global equity, at net asset value 1: |  |  |  |  |  |  |  |
Non-U.S. equity |  | 48,836 |  |  | — |  |  | — |  |  | — |
U.S. equity |  | 55,073 |  |  | — |  |  | — |  |  | — |
Total global equity |  | 103,909 |  |  | — |  |  | — |  |  | — |
Private equity (limited partnerships, at net asset value)1: |  |  |  |  |  |  |  |  |
Real assets |  | 15,466 |  |  | — |  |  | — |  |  | — |
Private equity |  | 1,615 |  |  | — |  |  | — |  |  | — |
Private credit |  | 1,108 |  |  | — |  |  | — |  |  | — |
Total private equity |  | 18,189 |  |  | — |  |  | — |  |  | — |
Total invested assets |  | $ | 316,987 |  |  | 193,057 |  |  | 1,832 |  |  | — |
December 31, 2015 |  |  |  | Fair Value Measurements at 12/31/15 Using
($ in thousands) |  | Assets Measured at Fair Value At 12/31/15 |  | Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) |  | Significant Other Observable Inputs (Level 2) |  | Significant Unobservable Inputs (Level 3)
Description |  |  |  |  |  |  |  |  |  |  |  |
Long-duration fixed income: |  |  |  |  |  |  |  |  |  |  |  |
Global asset allocation fund |  | $ | 33,565 |  |  | 33,565 |  |  | — |  |  | — |
Extended duration fixed income |  | 117,297 |  |  | 117,297 |  |  | — |  |  | — |
Total long duration fixed income |  | 150,862 |  |  | 150,862 |  |  | — |  |  | — |
Cash and short-term investments: |  |  |  |  |  |  |  |
Short-term investments |  | 1,600 |  |  | 1,600 |  |  | — |  |  | — |
Deposit administration contracts |  | 1,418 |  |  | — |  |  | 1,418 |  |  | — |
Total cash and short-term investments |  | 3,018 |  |  | 1,600 |  |  | 1,418 |  |  | — |
Global equity, at net asset value 1: |  |  |  |  |  |  |  |
Non-U.S. equity |  | 42,603 |  |  | — |  |  | — |  |  | — |
U.S. equity |  | 46,840 |  |  | — |  |  | — |  |  | — |
Total global equity |  | 89,443 |  |  | — |  |  | — |  |  | — |
Private equity (limited partnerships, at net asset value)1: |  |  |  |  |  |  |  |  |
Private equity |  | 2,626 |  |  | — |  |  | — |  |  | — |
Real assets |  | 2,514 |  |  | — |  |  | — |  |  | — |
Private credit |  | 1,318 |  |  | — |  |  | — |  |  | — |
Total private equity |  | 6,458 |  |  | — |  |  | — |  |  | — |
Total invested assets |  | $ | 249,781 |  |  | 152,462 |  |  | 1,418 |  |  | — |
1 In accordance with ASU 2015-07, certain investments that are measured at fair value using the net asset value per share (or its practical expedient) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to total Pension Plan invested assets.

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- Definition Tabular disclosure of the change in the benefit obligation, fair value of plan assets, and funded status of pension plans or other employee benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(b)(c) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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