Related Party Transactions	12 Months Ended
Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions William M. Rue, a Director of the Parent, is Chairman of, and owns more than 10% of the equity of, Chas. E. Rue & Son, Inc., t/a Rue Insurance, a general independent retail insurance agency ("Rue Insurance"). Rue Insurance is an appointed distribution partner of the Insurance Subsidiaries on terms and conditions similar to those of our other distribution partners, which includes the right to participate in the Agent Plan. Mr. Rue’s son is President, and an employee, of Rue Insurance, and owns more than 10% of the equity of Rue Insurance. Mr. Rue’s daughter is an employee of Rue Insurance. Our relationship with Rue Insurance has existed since 1928. Rue Insurance placed insurance policies with the Insurance Subsidiaries for its customers and itself. Direct premiums written associated with these policies were $10.1 million in 2018, $11.1 million in 2017, and $10.4 million in 2016. In return, the Insurance Subsidiaries paid standard market commissions, including supplemental commissions, to Rue Insurance of $2.1 million in 2018, $2.3 million in 2017, and $2.1 million in 2016. Amounts due to Rue Insurance at December 31, 2018 and December 31, 2017 were $0.4 million and $0.6 million, respectively. All contracts and transactions with Rue Insurance were consummated in the ordinary course of business on an arm's-length basis. In 2005, we established a private foundation, now named The Selective Insurance Group Foundation (the "Foundation"), under Section 501(c)(3) of the Internal Revenue Code. The Board of Directors of the Foundation is comprised of some of the Parent's officers. We made $0.5 million of contributions to the Foundation in 2018. We made no contributions to the Foundation in 2017 and 2016, respectively. BlackRock, Inc., a leading publicly traded investment management firm (“BlackRock”), has purchased our common shares in the ordinary course of its investment business and has previously filed Schedules 13G/A with the SEC. On January 31, 2019, BlackRock filed a Schedule 13G/A reporting beneficial ownership as of December 31, 2018, of 14.2% of our common stock. In connection with purchasing our common shares, BlackRock filed the necessary filings with insurance regulatory authorities. On the basis of those filings, BlackRock is deemed not to be a controlling person for the purposes of applicable insurance law. We are required to disclose related party information for our transactions with BlackRock. BlackRock is highly regulated, serves its clients as a fiduciary, and has a diverse platform of active (alpha) and index (beta) investment strategies across asset classes that enables it to tailor investment outcomes and asset allocation solutions for clients. BlackRock also offers the BlackRock Solutions^® investment and risk management technology platform, Aladdin^®, risk analytics, advisory, and technology services and solutions to a broad base of institutional and wealth management investors. We incurred expenses related to BlackRock for services rendered of $2.0 million in both 2018 and 2017, and $0.4 million in 2016. Amounts payable for such services at December 31, 2018 and December 31, 2017, were $1.0 million and $0.5 million, respectively. As part of our overall investment diversification, we invest in various BlackRock funds from time to time. The market value of these investments were $0.8 million at December 31, 2018, and $0.5 million at both December 31, 2017 and December 31, 2016. There were no material transactions related to these holdings in 2018 and 2017. During 2016, we sold $77.6 million of these investments, which resulted in a $1.1 million gain on our investment portfolio. In addition, we recorded $2.3 million of investment income on these funds in 2016. There were no amounts payable on the settlement of these investment transactions at December 31, 2018 or December 31, 2017. Our Pension Plan contained investments in BlackRock funds of $131.9 million at December 31, 2018 and $134.3 million at December 31, 2017. We recorded a net investment loss on these funds of $9.3 million in 2018, net investment income of $25.2 million in 2017, and net investment income of $8.5 million in 2016. In addition, our Deferred Compensation Plan and Retirement Savings Plan may offer our employees the option to invest in various BlackRock funds. All contracts and transactions with BlackRock were consummated in the ordinary course of business on an arm's-length basis. The Vanguard Group ("Vanguard"), one of the world's largest investment management companies, offers low cost mutual funds and exchange-trade funds ("ETFs"), as well as other investment related services. On January 10, 2019, Vanguard filed a Schedule 13G/A reporting beneficial ownership as of December 31, 2018, of 10.1% of our common stock. In connection with purchasing our common shares, Vanguard filed the necessary filings with insurance regulatory authorities. On the basis of those filings, we do not expect Vanguard to be deemed a controlling person for the purposes of applicable insurance law. We are required to disclose related party information for our transactions with Vanguard. As part of our overall investment diversification, we may invest in various Vanguard funds from time to time. During 2018, we purchased $11.5 million in a Vanguard ETF and recorded dividend income of $0.4 million, with no amounts payable on the settlement of this transaction at December 31, 2018. The market value of this fund in our investment portfolio at December 31, 2018 was $10.5 million. There were no transactions with Vanguard in 2017 and 2016. Our Pension Plan contained investments in Vanguard funds of $86.3 million at December 31, 2017, but no investment in these funds existed at December 31, 2018. We recorded a net investment loss on these funds of $5.5 million in 2018, net investment income of $9.1 million in 2017, and net investment income of $5.4 million in 2016. In addition, our Deferred Compensation Plan and Retirement Savings Plan may offer our employees the option to invest in various Vanguard funds. All transactions with Vanguard are consummated in the ordinary course of business on an arm's-length basis.

Related Party Transactions

William M. Rue, a Director of the Parent, is Chairman of, and owns more than 10% of the equity of, Chas. E. Rue & Son, Inc., t/a Rue Insurance, a general independent retail insurance agency ("Rue Insurance"). Rue Insurance is an appointed distribution partner of the Insurance Subsidiaries on terms and conditions similar to those of our other distribution partners, which includes the right to participate in the Agent Plan. Mr. Rue’s son is President, and an employee, of Rue Insurance, and owns more than 10% of the equity of Rue Insurance. Mr. Rue’s daughter is an employee of Rue Insurance. Our relationship with Rue Insurance has existed since 1928.

Rue Insurance placed insurance policies with the Insurance Subsidiaries for its customers and itself. Direct premiums written associated with these policies were $10.1 million in 2018, $11.1 million in 2017, and $10.4 million in 2016. In return, the Insurance Subsidiaries paid standard market commissions, including supplemental commissions, to Rue Insurance of $2.1 million in 2018, $2.3 million in 2017, and $2.1 million in 2016. Amounts due to Rue Insurance at December 31, 2018 and December 31, 2017 were $0.4 million and $0.6 million, respectively. All contracts and transactions with Rue Insurance were consummated in the ordinary course of business on an arm's-length basis.

In 2005, we established a private foundation, now named The Selective Insurance Group Foundation (the "Foundation"), under Section 501(c)(3) of the Internal Revenue Code. The Board of Directors of the Foundation is comprised of some of the Parent's officers. We made $0.5 million of contributions to the Foundation in 2018. We made no contributions to the Foundation in 2017 and 2016, respectively.

BlackRock, Inc., a leading publicly traded investment management firm (“BlackRock”), has purchased our common shares in the ordinary course of its investment business and has previously filed Schedules 13G/A with the SEC. On January 31, 2019, BlackRock filed a Schedule 13G/A reporting beneficial ownership as of December 31, 2018, of 14.2% of our common stock. In connection with purchasing our common shares, BlackRock filed the necessary filings with insurance regulatory authorities. On the basis of those filings, BlackRock is deemed not to be a controlling person for the purposes of applicable insurance law.

We are required to disclose related party information for our transactions with BlackRock. BlackRock is highly regulated, serves its clients as a fiduciary, and has a diverse platform of active (alpha) and index (beta) investment strategies across asset classes that enables it to tailor investment outcomes and asset allocation solutions for clients. BlackRock also offers the BlackRock Solutions^® investment and risk management technology platform, Aladdin^®, risk analytics, advisory, and technology services and solutions to a broad base of institutional and wealth management investors. We incurred expenses related to BlackRock for services rendered of $2.0 million in both 2018 and 2017, and $0.4 million in 2016. Amounts payable for such services at December 31, 2018 and December 31, 2017, were $1.0 million and $0.5 million, respectively.

As part of our overall investment diversification, we invest in various BlackRock funds from time to time. The market value of these investments were $0.8 million at December 31, 2018, and $0.5 million at both December 31, 2017 and December 31, 2016. There were no material transactions related to these holdings in 2018 and 2017. During 2016, we sold $77.6 million of these investments, which resulted in a $1.1 million gain on our investment portfolio. In addition, we recorded $2.3 million of investment income on these funds in 2016. There were no amounts payable on the settlement of these investment transactions at December 31, 2018 or December 31, 2017.

Our Pension Plan contained investments in BlackRock funds of $131.9 million at December 31, 2018 and $134.3 million at December 31, 2017. We recorded a net investment loss on these funds of $9.3 million in 2018, net investment income of $25.2 million in 2017, and net investment income of $8.5 million in 2016. In addition, our Deferred Compensation Plan and Retirement Savings Plan may offer our employees the option to invest in various BlackRock funds. All contracts and transactions with BlackRock were consummated in the ordinary course of business on an arm's-length basis.

The Vanguard Group ("Vanguard"), one of the world's largest investment management companies, offers low cost mutual funds and exchange-trade funds ("ETFs"), as well as other investment related services. On January 10, 2019, Vanguard filed a Schedule 13G/A reporting beneficial ownership as of December 31, 2018, of 10.1% of our common stock. In connection with purchasing our common shares, Vanguard filed the necessary filings with insurance regulatory authorities. On the basis of those filings, we do not expect Vanguard to be deemed a controlling person for the purposes of applicable insurance law.

We are required to disclose related party information for our transactions with Vanguard. As part of our overall investment diversification, we may invest in various Vanguard funds from time to time. During 2018, we purchased $11.5 million in a Vanguard ETF and recorded dividend income of $0.4 million, with no amounts payable on the settlement of this transaction at December 31, 2018. The market value of this fund in our investment portfolio at December 31, 2018 was $10.5 million. There were no transactions with Vanguard in 2017 and 2016.

Our Pension Plan contained investments in Vanguard funds of $86.3 million at December 31, 2017, but no investment in these funds existed at December 31, 2018. We recorded a net investment loss on these funds of $5.5 million in 2018, net investment income of $9.1 million in 2017, and net investment income of $5.4 million in 2016. In addition, our Deferred Compensation Plan and Retirement Savings Plan may offer our employees the option to invest in various Vanguard funds. All transactions with Vanguard are consummated in the ordinary course of business on an arm's-length basis.