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v3.19.3.a.u2

Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Investments | $ 6,688,654 | $ 5,960,651 |
Direct premiums written | 3,084,451 | 2,890,633 | $ 2,733,459
Contributions to the Selective Insurance Group Foundation | 1,300 | 500 | 0
Costs and Expenses, Related Party | 2,200 | 2,000 | 2,000
Due to Related Parties | $ 1,100 | 1,000 |
Related Party Insurance Agency [Member] |  |  |
Equity ownership percentage of director of parent of general independent retail insurance agency | 10.00% |  |
Equity Ownership Percentage Of Son Of Director Of Parent | 10.00% |  |
Direct premiums written | $ 11,000 | 10,100 | 11,100
Commissions paid to Rue Insurance | 2,000 | 2,100 | 2,300
Due to Related Parties, Current | $ 300 | $ 400 |
Vanguard Group [Member] |  |  |
Percentage Common Stock Owned by Related Party | 9.40% | 10.10% |
Related Party Transaction, Purchases from Related Party |  | $ 11,500 |
Sale of Related Party Investments | $ 11,800 |  |
Investment Income, Dividend | 200 | 400 |
Related Party Capital Gains (Losses) | $ 1,300 |  |
BlackRock Inc [Member] |  |  |
Percentage Common Stock Owned by Related Party | 11.70% |  |
Investments |  |  | 500
Related Party Transaction, Purchases from Related Party | $ 21,700 | 41,400 |
Sale of Related Party Investments | 59,500 |  |
Net realized and unrealized gain (loss) | 5,700 | (3,600) |
Investment Income (Loss), Net | 800 |  |
Retirement Income Plan [Member] | Vanguard Group [Member] |  |  |
Investments |  |  | 86,300
Related Party Transaction, Purchases from Related Party |  | 8,400 | 5,200
Sale of Related Party Investments |  | 85,400 |
Investment Income (Loss), Net |  | (5,500) | 9,100
Retirement Income Plan [Member] | BlackRock Inc [Member] |  |  |
Investments | 144,200 | 131,900 |
Related Party Transaction, Purchases from Related Party | 19,700 | 132,500 | 10,000
Sale of Related Party Investments | 44,100 | 125,600 | 4,100
Investment Income (Loss), Net | $ 36,700 | $ 9,300 | $ 25,200

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