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Investments (Tables) | 9 Months Ended
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Sep. 30, 2018
Investments [Line Items] |
Schedule of Held-to-maturity Securities |
September 30, 2018 |  |  |  |  |  |  |  |  |  |  |  |
($ in thousands) |  | Amortized Cost |  | Net Unrealized Gains (Losses) |  | Carrying Value |  | Unrecognized Holding Gains |  | Unrecognized Holding Losses |  | Fair Value
Obligations of states and political subdivisions |  | $ | 21,834 |  |  | 36 |  |  | 21,870 |  |  | 526 |  |  | — |  |  | 22,396 |
Corporate securities |  | 22,798 |  |  | (86 | ) |  | 22,712 |  |  | 1,132 |  |  | — |  |  | 23,844 |
Total HTM fixed income securities |  | $ | 44,632 |  |  | (50 | ) |  | 44,582 |  |  | 1,658 |  |  | — |  |  | 46,240 |
December 31, 2017 |  |  |  |  |  |  |  |  |  |  |  |
($ in thousands) |  | Amortized Cost |  | Net Unrealized Gains (Losses) |  | Carrying Value |  | Unrecognized Holding Gains |  | Unrecognized Holding Losses |  | Fair Value
Obligations of states and political subdivisions |  | $ | 25,154 |  |  | 84 |  |  | 25,238 |  |  | 1,023 |  |  | — |  |  | 26,261 |
Corporate securities |  | 16,996 |  |  | (105 | ) |  | 16,891 |  |  | 1,003 |  |  | (55 | ) |  | 17,839 |
Total HTM fixed income securities |  | $ | 42,150 |  |  | (21 | ) |  | 42,129 |  |  | 2,026 |  |  | (55 | ) |  | 44,100 |
Schedule of Available-for-sale Securities |
September 30, 2018 |  |  |  |  |  |  |  |
($ in thousands) |  | Cost/ Amortized Cost |  | Unrealized Gains |  | Unrealized Losses |  | Fair Value
AFS fixed income securities: |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 97,304 |  |  | 306 |  |  | (1,148 | ) |  | 96,462 |
Foreign government |  | 18,015 |  |  | 88 |  |  | (120 | ) |  | 17,983 |
Obligations of states and political subdivisions |  | 1,161,322 |  |  | 10,848 |  |  | (7,261 | ) |  | 1,164,909 |
Corporate securities |  | 1,662,613 |  |  | 6,342 |  |  | (19,302 | ) |  | 1,649,653 |
Collateralized loan obligations and other asset-backed securities ("CLO and other ABS") |  | 772,738 |  |  | 4,571 |  |  | (2,540 | ) |  | 774,769 |
Commercial mortgage-backed securities ("CMBS") |  | 495,208 |  |  | 328 |  |  | (5,987 | ) |  | 489,549 |
Residential mortgage-backed securities (“RMBS”) |  | 1,009,764 |  |  | 2,670 |  |  | (15,603 | ) |  | 996,831 |
Total AFS securities |  | $ | 5,216,964 |  |  | 25,153 |  |  | (51,961 | ) |  | 5,190,156 |
December 31, 2017 |  |  |  |  |  |  |  |
($ in thousands) |  | Cost/ Amortized Cost |  | Unrealized Gains |  | Unrealized Losses |  | Fair Value
AFS fixed income securities: |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 49,326 |  |  | 647 |  |  | (233 | ) |  | 49,740 |
Foreign government |  | 18,040 |  |  | 526 |  |  | (11 | ) |  | 18,555 |
Obligations of states and political subdivisions |  | 1,539,307 |  |  | 44,245 |  |  | (582 | ) |  | 1,582,970 |
Corporate securities |  | 1,588,339 |  |  | 30,891 |  |  | (1,762 | ) |  | 1,617,468 |
CLO and other ABS |  | 789,152 |  |  | 6,508 |  |  | (202 | ) |  | 795,458 |
CMBS |  | 382,727 |  |  | 1,563 |  |  | (841 | ) |  | 383,449 |
RMBS |  | 709,825 |  |  | 6,487 |  |  | (1,430 | ) |  | 714,882 |
Total AFS fixed income securities |  | 5,076,716 |  |  | 90,867 |  |  | (5,061 | ) |  | 5,162,522 |
AFS equity securities: |  |  |  |  |  |  |  |
Common stock |  | 129,696 |  |  | 38,287 |  |  | (226 | ) |  | 167,757 |
Preferred stock |  | 14,115 |  |  | 904 |  |  | (71 | ) |  | 14,948 |
Total AFS equity securities |  | 143,811 |  |  | 39,191 |  |  | (297 | ) |  | 182,705 |
Total AFS securities |  | $ | 5,220,527 |  |  | 130,058 |  |  | (5,358 | ) |  | 5,345,227 |
Schedule of Fair Value and Gross Pre-Tax Net Unrealized/Unrecognized Loss of Securities by Length of Time, AFS |
September 30, 2018 |  | Less than 12 months |  | 12 months or longer |  | Total
($ in thousands) |  | Fair Value |  | Unrealized Losses 1 |  | Fair Value |  | Unrealized Losses 1 |  | Fair Value |  | Unrealized Losses 1
AFS fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 26,414 |  |  | (843 | ) |  | 8,497 |  |  | (305 | ) |  | 34,911 |  |  | (1,148 | )
Foreign government |  | 7,281 |  |  | (120 | ) |  | — |  |  | — |  |  | 7,281 |  |  | (120 | )
Obligations of states and political subdivisions |  | 411,980 |  |  | (7,008 | ) |  | 6,397 |  |  | (253 | ) |  | 418,377 |  |  | (7,261 | )
Corporate securities |  | 1,140,349 |  |  | (19,052 | ) |  | 6,373 |  |  | (250 | ) |  | 1,146,722 |  |  | (19,302 | )
CLO and other ABS |  | 497,809 |  |  | (2,479 | ) |  | 4,335 |  |  | (61 | ) |  | 502,144 |  |  | (2,540 | )
CMBS |  | 376,359 |  |  | (5,940 | ) |  | 2,340 |  |  | (47 | ) |  | 378,699 |  |  | (5,987 | )
RMBS |  | 699,336 |  |  | (14,727 | ) |  | 19,183 |  |  | (876 | ) |  | 718,519 |  |  | (15,603 | )
Total AFS securities |  | $ | 3,159,528 |  |  | (50,169 | ) |  | 47,125 |  |  | (1,792 | ) |  | 3,206,653 |  |  | (51,961 | )
December 31, 2017 |  | Less than 12 months |  | 12 months or longer |  | Total
($ in thousands) |  | Fair Value |  | Unrealized Losses 1 |  | Fair Value |  | Unrealized Losses 1 |  | Fair Value |  | Unrealized Losses 1
AFS fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 23,516 |  |  | (233 | ) |  | 250 |  |  | — |  |  | 23,766 |  |  | (233 | )
Foreign government |  | 1,481 |  |  | (11 | ) |  | — |  |  | — |  |  | 1,481 |  |  | (11 | )
Obligations of states and political subdivisions |  | 107,514 |  |  | (422 | ) |  | 14,139 |  |  | (160 | ) |  | 121,653 |  |  | (582 | )
Corporate securities |  | 238,326 |  |  | (1,744 | ) |  | 3,228 |  |  | (18 | ) |  | 241,554 |  |  | (1,762 | )
CLO and other ABS |  | 74,977 |  |  | (196 | ) |  | 1,655 |  |  | (6 | ) |  | 76,632 |  |  | (202 | )
CMBS |  | 154,267 |  |  | (773 | ) |  | 5,214 |  |  | (68 | ) |  | 159,481 |  |  | (841 | )
RMBS |  | 269,485 |  |  | (1,285 | ) |  | 11,200 |  |  | (145 | ) |  | 280,685 |  |  | (1,430 | )
Total AFS fixed income securities |  | 869,566 |  |  | (4,664 | ) |  | 35,686 |  |  | (397 | ) |  | 905,252 |  |  | (5,061 | )
AFS equity securities: |  |  |  |  |  |  |  |  |  |  |  |
Common stock |  | 4,727 |  |  | (226 | ) |  | — |  |  | — |  |  | 4,727 |  |  | (226 | )
Preferred stock |  | 3,833 |  |  | (71 | ) |  | — |  |  | — |  |  | 3,833 |  |  | (71 | )
Total AFS equity securities |  | 8,560 |  |  | (297 | ) |  | — |  |  | — |  |  | 8,560 |  |  | (297 | )
Total AFS |  | $ | 878,126 |  |  | (4,961 | ) |  | 35,686 |  |  | (397 | ) |  | 913,812 |  |  | (5,358 | )
1 Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI.
Schedule of Fixed Maturity Securities By Contractual Maturities |
|  | AFS |  | HTM
($ in thousands) |  | Fair Value |  | Carrying Value |  | Fair Value
Due in one year or less |  | $ | 176,545 |  |  | 14,017 |  |  | 14,150 |
Due after one year through five years |  | 2,107,663 |  |  | 20,518 |  |  | 21,926 |
Due after five years through 10 years |  | 2,759,167 |  |  | 10,047 |  |  | 10,164 |
Due after 10 years |  | 146,781 |  |  | — |  |  | — |
Total fixed income securities |  | $ | 5,190,156 |  |  | 44,582 |  |  | 46,240 |
Schedule of Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy |
Other Investments |  | September 30, 2018 |  | December 31, 2017
($ in thousands) |  | Carrying Value |  | Remaining Commitment |  | Maximum Exposure to Loss 1 |  | Carrying Value |  | Remaining Commitment |  | Maximum Exposure to Loss 1
Alternative Investments |  |  |  |  |  |  |  |  |  |  |  |  |  |
Private equity |  | $ | 75,508 |  |  | 99,346 |  |  | 174,854 |  |  | 52,251 |  |  | 99,026 |  |  | 151,277 |
Private credit |  | 37,525 |  |  | 85,747 |  |  | 123,272 |  |  | 37,743 |  |  | 94,959 |  |  | 132,702 |
Real assets |  | 25,214 |  |  | 33,088 |  |  | 58,302 |  |  | 25,379 |  |  | 27,014 |  |  | 52,393 |
Total alternative investments |  | 138,247 |  |  | 218,181 |  |  | 356,428 |  |  | 115,373 |  |  | 220,999 |  |  | 336,372 |
Other securities |  | 25,683 |  |  | — |  |  | 25,683 |  |  | 16,895 |  |  | — |  |  | 16,895 |
Total other investments |  | $ | 163,930 |  |  | 218,181 |  |  | 382,111 |  |  | 132,268 |  |  | 220,999 |  |  | 353,267 |
1 The maximum exposure to loss includes both the carry value of these investments and the related unfunded commitments. In addition, tax credits that have been previously recognized in Other securities are subject to the risk of recapture, which we do not consider significant.
Schedule of Aggregated Summarized Income Statement Financial Information For Partnerships In Our Alternative Investment Portfolio |
Income Statement Information |  | Quarter ended September 30, |  | Nine Months ended September 30,
($ in millions) |  | 2018 |  | 2017 |  | 2018 |  | 2017
Net investment income (loss) |  | $ | 11.9 |  |  | 0.6 |  |  | (29.9 | ) |  | (61.8 | )
Realized gains (losses) |  | 124.8 |  |  | 43.3 |  |  | 1,348.3 |  |  | (261.0 | )
Net change in unrealized appreciation |  | 1,434.3 |  |  | 1,296.3 |  |  | 695.8 |  |  | 3,186.3 |
Net gain |  | $ | 1,571.0 |  |  | 1,340.2 |  |  | 2,014.2 |  |  | 2,863.5 |
Selective’s insurance subsidiaries’ alternative investments gain |  | $ | 7.1 |  |  | 2.7 |  |  | 10.6 |  |  | 9.5 |
Schedule of Securities Pledged As Collateral |
($ in millions) |  | FHLBI Collateral |  | FHLBNY Collateral |  | State and Regulatory Deposits |  | Total
U.S. government and government agencies |  | $ | — |  |  | — |  |  | 22.2 |  |  | 22.2 |
Obligations of states and political subdivisions |  | — |  |  | — |  |  | 3.8 |  |  | 3.8 |
CMBS |  | 7.2 |  |  | 9.4 |  |  | — |  |  | 16.6 |
RMBS |  | 57.8 |  |  | 76.3 |  |  | — |  |  | 134.1 |
Total pledged as collateral |  | $ | 65.0 |  |  | 85.7 |  |  | 26.0 |  |  | 176.7 |
Schedule of Pre-Tax Net Investment Income Earned |
|  | Quarter ended September 30, |  | Nine Months ended September 30,
($ in thousands) |  | 2018 |  | 2017 |  | 2018 |  | 2017
Fixed income securities |  | $ | 45,088 |  |  | 38,865 |  |  | 130,903 |  |  | 113,424 |
Equity securities |  | 2,079 |  |  | 1,605 |  |  | 5,876 |  |  | 4,492 |
Short-term investments |  | 867 |  |  | 396 |  |  | 2,001 |  |  | 1,023 |
Other investments |  | 7,211 |  |  | 2,659 |  |  | 10,868 |  |  | 9,493 |
Investment expenses |  | (2,802 | ) |  | (3,079 | ) |  | (8,421 | ) |  | (9,137 | )
Net investment income earned |  | $ | 52,443 |  |  | 40,446 |  |  | 141,227 |  |  | 119,295 |
Schedule of Components of Net Realized and Unrealized Gains and Losses Excluding OTTI Charges |
|  | Quarter ended September 30, |  | Nine Months ended September 30,
($ in thousands) |  | 2018 |  | 2017 |  | 2018 |  | 2017
Net realized (losses) gains on the disposals of securities: |  |  |  |  |  |  |  |
Fixed income securities |  | $ | (9,413 | ) |  | 1,996 |  |  | (13,922 | ) |  | 6,566 |
Equity securities |  | 8,665 |  |  | 4,875 |  |  | 17,960 |  |  | 5,225 |
Short-term investments |  | 2 |  |  | — |  |  | 1 |  |  | — |
Other investments |  | (5 | ) |  | — |  |  | (5 | ) |  | 461 |
Net realized gains on the disposal of securities |  | (751 | ) |  | 6,871 |  |  | 4,034 |  |  | 12,252 |
OTTI charges |  | (1,426 | ) |  | (73 | ) |  | (5,459 | ) |  | (4,765 | )
Net realized (losses) gains |  | (2,177 | ) |  | 6,798 |  |  | (1,425 | ) |  | 7,487 |
Unrealized (losses) recognized in income on equity securities 1 |  | (2,610 | ) |  | — |  |  | (15,563 | ) |  | — |
Total net realized and unrealized investment (losses) gains |  | $ | (4,787 | ) |  | 6,798 |  |  | $ | (16,988 | ) |  | 7,487 |
1 Includes unrealized holding gains (losses) of: (i) $5.5 million in Third Quarter 2018 and $4.2 million in Nine Months 2018 on equity securities remaining in our portfolio as of September 30, 2018; and (ii) $(8.1) million in Third Quarter 2018 and $(19.8) million in Nine Months 2018 on equity securities sold during the respective periods.
Schedule of Realized Gains and Losses on Disposals of Securities |
|  | Quarter ended September 30, |  | Nine Months ended September 30,
($ in thousands) |  | 2018 |  | 2017 |  | 2018 |  | 2017
HTM fixed income securities |  |  |  |  |  |  |  |
Gains |  | $ | — |  |  | — |  |  | 2 |  |  | 44 |
Losses |  | — |  |  | — |  |  | — |  |  | (1 | )
AFS fixed income securities |  |  |  |  |  |  |  |  |  |
Gains |  | 462 |  |  | 2,070 |  |  | 5,056 |  |  | 8,337 |
Losses |  | (9,875 | ) |  | (74 | ) |  | (18,980 | ) |  | (1,814 | )
Equity securities |  |  |  |  |  |  |  |  |  |
Gains |  | 10,584 |  |  | 4,875 |  |  | 20,209 |  |  | 5,225 |
Losses |  | (1,919 | ) |  | — |  |  | (2,249 | ) |  | — |
Short-term investments |  |  |  |  |  |  |  |
Gains |  | 3 |  |  | — |  |  | 6 |  |  | 2 |
Losses |  | (1 | ) |  | — |  |  | (5 | ) |  | (2 | )
Other investments |  |  |  |  |  |  |  |
Gains |  | — |  |  | — |  |  | — |  |  | 480 |
Losses |  | (5 | ) |  | — |  |  | (5 | ) |  | (19 | )
Total net realized gains (losses) on disposals of securities |  | $ | (751 | ) |  | 6,871 |  |  | 4,034 |  |  | 12,252 |

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