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Investments (Tables) | 12 Months Ended
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Dec. 31, 2016
Investment [Line Items] |
Schedule of Unrealized Gains On Investments |
($ in thousands) |  | 2016 |  | 2015 |  | 2014
AFS securities: |  |  |  |  |  |  |  |  |
Fixed income securities |  | $ | 38,781 |  |  | 55,689 |  |  | 90,336 |
Equity securities |  | 25,864 |  |  | 13,235 |  |  | 32,389 |
Total AFS securities |  | 64,645 |  |  | 68,924 |  |  | 122,725 |
HTM securities: |  |  |  |  |  |  |  |  |
Fixed income securities |  | 159 |  |  | 300 |  |  | 958 |
Total HTM securities |  | 159 |  |  | 300 |  |  | 958 |
Total net unrealized gains |  | 64,804 |  |  | 69,224 |  |  | 123,683 |
Deferred income tax expense |  | (22,681 | ) |  | (24,228 | ) |  | (43,289 | )
Net unrealized gains, net of deferred income tax |  | 42,123 |  |  | 44,996 |  |  | 80,394 |
(Decrease) increase in net unrealized gains in OCI, net of deferred income tax |  | $ | (2,873 | ) |  | (35,398 | ) |  | 28,890 |
Schedule of Held-to-maturity Securities |
December 31, 2016 |  |  |  | Net |  |  |  |  |  |  |  |
|  |  |  | Unrealized |  |  |  | Unrecognized |  | Unrecognized |  |
|  | Amortized |  | Gains |  | Carrying |  | Holding |  | Holding |  | Fair
($ in thousands) |  | Cost |  | (Losses) |  | Value |  | Gains |  | Losses |  | Value
Obligations of state and political subdivisions |  | $ | 77,466 |  |  | 317 |  |  | 77,783 |  |  | 2,133 |  |  | — |  |  | 79,916 |
Corporate securities |  | 22,711 |  |  | (143 | ) |  | 22,568 |  |  | 1,665 |  |  | (158 | ) |  | 24,075 |
CMBS |  | 1,220 |  |  | (15 | ) |  | 1,205 |  |  | 15 |  |  | — |  |  | 1,220 |
Total HTM fixed income securities |  | $ | 101,397 |  |  | 159 |  |  | 101,556 |  |  | 3,813 |  |  | (158 | ) |  | 105,211 |
December 31, 2015 |  |  |  | Net |  |  |  |  |  |  |  |
|  |  |  | Unrealized |  |  |  | Unrecognized |  | Unrecognized |  |
|  | Amortized |  | Gains |  | Carrying |  | Holding |  | Holding |  | Fair
($ in thousands) |  | Cost |  | (Losses) |  | Value |  | Gains |  | Losses |  | Value
Obligations of state and political subdivisions |  | 175,269 |  |  | 848 |  |  | 176,117 |  |  | 5,763 |  |  | — |  |  | 181,880 |
Corporate securities |  | 20,228 |  |  | (185 | ) |  | 20,043 |  |  | 1,972 |  |  | — |  |  | 22,015 |
CLO and other ABS |  | 1,030 |  |  | (120 | ) |  | 910 |  |  | 118 |  |  | — |  |  | 1,028 |
CMBS |  | 4,527 |  |  | (243 | ) |  | 4,284 |  |  | 337 |  |  | — |  |  | 4,621 |
Total HTM fixed income securities |  | $ | 201,054 |  |  | 300 |  |  | 201,354 |  |  | 8,190 |  |  | — |  |  | 209,544 |
Schedule of Available For Sale Securities |
December 31, 2016 |  |  |  |  |  |  |  |
|  | Cost/ |  |  |  |  |  |
|  | Amortized |  | Unrealized |  | Unrealized |  | Fair
($ in thousands) |  | Cost |  | Gains |  | Losses |  | Value
AFS fixed income securities: |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 75,139 |  |  | 2,230 |  |  | (36 | ) |  | 77,333 |
Foreign government |  | 26,559 |  |  | 322 |  |  | (16 | ) |  | 26,865 |
Obligations of states and political subdivisions |  | 1,366,287 |  |  | 18,610 |  |  | (5,304 | ) |  | 1,379,593 |
Corporate securities |  | 1,976,556 |  |  | 27,057 |  |  | (5,860 | ) |  | 1,997,753 |
CLO and other ABS |  | 527,876 |  |  | 1,439 |  |  | (355 | ) |  | 528,960 |
CMBS |  | 256,356 |  |  | 1,514 |  |  | (1,028 | ) |  | 256,842 |
RMBS |  | 524,986 |  |  | 3,006 |  |  | (2,798 | ) |  | 525,194 |
Total AFS fixed income securities |  | 4,753,759 |  |  | 54,178 |  |  | (15,397 | ) |  | 4,792,540 |
AFS equity securities: |  |  |  |  |  |  |  |
Common stock |  | 104,663 |  |  | 26,250 |  |  | (305 | ) |  | 130,608 |
Preferred stock |  | 16,226 |  |  | 274 |  |  | (355 | ) |  | 16,145 |
Total AFS equity securities |  | 120,889 |  |  | 26,524 |  |  | (660 | ) |  | 146,753 |
Total AFS securities |  | $ | 4,874,648 |  |  | 80,702 |  |  | (16,057 | ) |  | 4,939,293 |
December 31, 2015 |  |  |  |  |  |  |  |
|  | Cost/ |  |  |  |  |  |
|  | Amortized |  | Unrealized |  | Unrealized |  | Fair
($ in thousands) |  | Cost |  | Gains |  | Losses |  | Value
AFS fixed income securities: |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 99,485 |  |  | 4,721 |  |  | (91 | ) |  | 104,115 |
Foreign government |  | 14,885 |  |  | 298 |  |  | (2 | ) |  | 15,181 |
Obligations of states and political subdivisions |  | 1,314,779 |  |  | 44,523 |  |  | (160 | ) |  | 1,359,142 |
Corporate securities |  | 1,892,296 |  |  | 23,407 |  |  | (15,521 | ) |  | 1,900,182 |
CLO and other ABS |  | 244,541 |  |  | 531 |  |  | (918 | ) |  | 244,154 |
CMBS |  | 245,252 |  |  | 750 |  |  | (2,410 | ) |  | 243,592 |
RMBS |  | 541,276 |  |  | 4,274 |  |  | (3,713 | ) |  | 541,837 |
Total AFS fixed income securities |  | 4,352,514 |  |  | 78,504 |  |  | (22,815 | ) |  | 4,408,203 |
AFS equity securities: |  |  |  |  |  |  |  |
Common stock |  | 181,991 |  |  | 14,796 |  |  | (1,998 | ) |  | 194,789 |
Preferred stock |  | 11,825 |  |  | 477 |  |  | (40 | ) |  | 12,262 |
Total AFS equity securities |  | 193,816 |  |  | 15,273 |  |  | (2,038 | ) |  | 207,051 |
Total AFS securities |  | $ | 4,546,330 |  |  | 93,777 |  |  | (24,853 | ) |  | 4,615,254 |
Schedule of Fair Value and Gross Pre-Tax Net Unrealized/Unrecognized Loss of Securities by Length of Time |
December 31, 2016 |  | Less than 12 months |  | 12 months or longer |  | Total
($ in thousands) |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses
AFS fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 6,419 |  |  | (36 | ) |  | — |  |  | — |  |  | 6,419 |  |  | (36 | )
Foreign government |  | 13,075 |  |  | (16 | ) |  | — |  |  | — |  |  | 13,075 |  |  | (16 | )
Obligations of states and political subdivisions |  | 306,509 |  |  | (5,304 | ) |  | — |  |  | — |  |  | 306,509 |  |  | (5,304 | )
Corporate securities |  | 462,902 |  |  | (5,771 | ) |  | 4,913 |  |  | (89 | ) |  | 467,815 |  |  | (5,860 | )
CLO and other ABS |  | 189,795 |  |  | (354 | ) |  | 319 |  |  | (1 | ) |  | 190,114 |  |  | (355 | )
CMBS |  | 82,492 |  |  | (1,021 | ) |  | 1,645 |  |  | (7 | ) |  | 84,137 |  |  | (1,028 | )
RMBS |  | 279,480 |  |  | (2,489 | ) |  | 8,749 |  |  | (309 | ) |  | 288,229 |  |  | (2,798 | )
Total AFS fixed income securities |  | 1,340,672 |  |  | (14,991 | ) |  | 15,626 |  |  | (406 | ) |  | 1,356,298 |  |  | (15,397 | )
AFS equity securities: |  |  |  |  |  |  |  |  |  |  |  |
Common stock |  | 11,271 |  |  | (305 | ) |  | — |  |  | — |  |  | 11,271 |  |  | (305 | )
Preferred stock |  | 6,168 |  |  | (355 | ) |  | — |  |  | — |  |  | 6,168 |  |  | (355 | )
Total AFS equity securities |  | 17,439 |  |  | (660 | ) |  | — |  |  | — |  |  | 17,439 |  |  | (660 | )
Total AFS securities |  | $ | 1,358,111 |  |  | (15,651 | ) |  | 15,626 |  |  | (406 | ) |  | 1,373,737 |  |  | (16,057 | )
December 31, 2015 |  | Less than 12 months |  | 12 months or longer |  | Total
($ in thousands) |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses
AFS fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. government and government agencies |  | $ | 16,006 |  |  | (87 | ) |  | 396 |  |  | (4 | ) |  | $ | 16,402 |  |  | $ | (91 | )
Foreign government |  | 1,067 |  |  | (2 | ) |  | — |  |  | — |  |  | 1,067 |  |  | (2 | )
Obligations of states and political subdivisions |  | 28,617 |  |  | (160 | ) |  | — |  |  | — |  |  | 28,617 |  |  | (160 | )
Corporate securities |  | 761,479 |  |  | (12,671 | ) |  | 50,382 |  |  | (2,850 | ) |  | 811,861 |  |  | (15,521 | )
CLO and other ABS |  | 197,477 |  |  | (807 | ) |  | 12,022 |  |  | (111 | ) |  | 209,499 |  |  | (918 | )
CMBS |  | 146,944 |  |  | (2,196 | ) |  | 15,385 |  |  | (214 | ) |  | 162,329 |  |  | (2,410 | )
RMBS |  | 264,914 |  |  | (1,992 | ) |  | 63,395 |  |  | (1,721 | ) |  | 328,309 |  |  | (3,713 | )
Total AFS fixed income securities |  | 1,416,504 |  |  | (17,915 | ) |  | 141,580 |  |  | (4,900 | ) |  | 1,558,084 |  |  | (22,815 | )
AFS equity securities: |  |  |  |  |  |  |  |  |  |  |  |
Common stock |  | 31,148 |  |  | (1,998 | ) |  | — |  |  | — |  |  | 31,148 |  |  | (1,998 | )
Preferred stock |  | 1,531 |  |  | (40 | ) |  | — |  |  | — |  |  | 1,531 |  |  | (40 | )
Total AFS equity securities |  | 32,679 |  |  | (2,038 | ) |  | — |  |  | — |  |  | 32,679 |  |  | (2,038 | )
Total AFS securities |  | $ | 1,449,183 |  |  | (19,953 | ) |  | 141,580 |  |  | (4,900 | ) |  | $ | 1,590,763 |  |  | $ | (24,853 | )
Schedule of Other Investment Portfolio by Strategy and the Remaining Commitment Amount Associated With Each Strategy |
Other Investments |  | December 31, 2016 |  | December 31, 2015
($ in thousands) |  | Carrying Value |  | Remaining Commitment |  | Maximum Exposure to Loss 1 |  | Carrying Value |  | Remaining Commitment |  | Maximum Exposure to Loss 1
Alternative Investments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Private equity |  | $ | 41,135 |  |  | 76,774 |  |  | 117,909 |  |  | 35,088 |  |  | 30,204 |  |  | 65,292 |
Private credit |  | 28,193 |  |  | 40,613 |  |  | 68,806 |  |  | 13,246 |  |  | 15,129 |  |  | 28,375 |
Real assets |  | 14,486 |  |  | 22,899 |  |  | 37,385 |  |  | 19,500 |  |  | 25,820 |  |  | 45,320 |
Total alternative investments |  | 83,814 |  |  | 140,286 |  |  | 224,100 |  |  | 67,834 |  |  | 71,153 |  |  | 138,987 |
Other securities |  | 18,583 |  |  | 3,400 |  |  | 21,983 |  |  | 10,008 |  |  | 3,200 |  |  | 13,208 |
Total other investments |  | $ | 102,397 |  |  | 143,686 |  |  | 246,083 |  |  | 77,842 |  |  | 74,353 |  |  | 152,195 |
Schedule of Aggregated Summarized Balance Sheet Financial Information For Partnerhips In Our Alternative Investment Portfolio |
Balance Sheet Information |  |  |  |
September 30, |  |  |  |
($ in millions) |  | 2016 |  | 2015
Investments |  | $ | 11,244 |  |  | 7,527 |
Total assets |  | 12,075 |  |  | 8,515 |
Total liabilities |  | 1,802 |  |  | 316 |
Total partners’ capital |  | 10,273 |  |  | 8,199 |
Schedule of Aggregated Summarized Income Statement Financial Information For Partnerhips In Our Alternative Investment Portfolio |
Income Statement Information |  |  |  |  |  |
12 months ended September 30, |  |  |  |  |  |
($ in millions) |  | 2016 |  | 2015 |  | 2014
Net investment income |  | $ | (44 | ) |  | 129 |  |  | 226 |
Realized gains |  | 1,374 |  |  | 1,187 |  |  | 581 |
Net change in unrealized (depreciation) appreciation |  | (719 | ) |  | (1,364 | ) |  | 1,098 |
Net income |  | $ | 611 |  |  | (48 | ) |  | 1,905 |
Insurance Subsidiaries' alternative investments income |  | 3.1 |  |  | (1.9 | ) |  | 13.6 |
Schedule Of Securities Pledged As Collateral | The following table summarizes the market value of these securities at December 31, 2016:
($ in millions) |  | FHLBI Collateral |  | FHLBNY Collateral |  | State and Regulatory Deposits |  | Total
U.S. government and government agencies |  | $ | 7.4 |  |  | — |  |  | 24.8 |  |  | 32.2 |
CMBS |  | 0.5 |  |  | — |  |  | — |  |  | 0.5 |
RMBS |  | 59.6 |  |  | 58.2 |  |  | — |  |  | 117.8 |
Total pledged as collateral |  | $ | 67.5 |  |  | 58.2 |  |  | 24.8 |  |  | 150.5 |
Schedule of Components of Net Investment Income Earned |
($ in thousands) |  | 2016 |  | 2015 |  | 2014
Fixed income securities |  | $ | 129,306 |  |  | 123,230 |  |  | 126,489 |
Equity securities |  | 7,368 |  |  | 9,161 |  |  | 7,449 |
Short-term investments |  | 686 |  |  | 112 |  |  | 66 |
Other investments |  | 2,940 |  |  | (1,890 | ) |  | 13,580 |
Investment expenses |  | (9,546 | ) |  | (9,297 | ) |  | (8,876 | )
Net investment income earned |  | $ | 130,754 |  |  | 121,316 |  |  | 138,708 |
Schedule of OTTI by Asset Type |
2016 |  |  |  |  |  | Recognized in Earnings
($ in thousands) |  | Gross |  | Included in OCI |
AFS fixed income securities: |  |  |  |  |  |
Obligations of states and political subdivisions |  | $ | 2,797 |  |  | — |  |  | 2,797 |
Corporate securities |  | 1,880 |  |  | — |  |  | 1,880 |
CLO and other ABS |  | 19 |  |  | — |  |  | 19 |
CMBS |  | 220 |  |  | — |  |  | 220 |
RMBS |  | 275 |  |  | 10 |  |  | 265 |
Total AFS fixed income securities |  | 5,191 |  |  | 10 |  |  | 5,181 |
AFS equity securities: |  |  |  |  |  |
Common stock |  | 3,316 |  |  | — |  |  | 3,316 |
Preferred stock |  | 2 |  |  | — |  |  | 2 |
Total AFS equity securities |  | 3,318 |  |  | — |  |  | 3,318 |
Total OTTI losses |  | $ | 8,509 |  |  | 10 |  |  | 8,499 |
2015 |  |  |  |  |  | Recognized in Earnings
($ in thousands) |  | Gross |  | Included in OCI |
AFS fixed income securities: |  |  |  |  |  |
Corporate securities |  | $ | 2,188 |  |  | — |  |  | 2,188 |
RMBS |  | 1 |  |  | — |  |  | 1 |
Total AFS fixed income securities |  | 2,189 |  |  | — |  |  | 2,189 |
AFS equity securities: |  |  |  |  |  |
Common stock |  | 15,996 |  |  | — |  |  | 15,996 |
Preferred stock |  | 181 |  |  | — |  |  | 181 |
Total AFS equity securities |  | 16,177 |  |  | — |  |  | 16,177 |
Total OTTI losses |  | $ | 18,366 |  |  | — |  |  | 18,366 |
2014 |  |  |  |  |  | Recognized in Earnings
($ in thousands) |  | Gross |  | Included in OCI |
AFS fixed income securities: |  |  |  |  |  |  |  |  |
RMBS |  | $ | 7 |  |  | — |  |  | 7 |
Total AFS fixed income securities |  | 7 |  |  | — |  |  | 7 |
AFS equity securities: |  |  |  |  |  |
Common stock |  | 10,517 |  |  | — |  |  | 10,517 |
Total AFS equity securities |  | 10,517 |  |  | — |  |  | 10,517 |
Other investments |  | 580 |  |  | — |  |  | 580 |
Total OTTI losses |  | $ | 11,104 |  |  | — |  |  | 11,104 |
Schedule of Components of Net Realized Gains Excluding OTTI Charges |
($ in thousands) |  | 2016 |  | 2015 |  | 2014
HTM fixed income securities |  |  |  |  |  |  |  |  |
Gains |  | $ | 3 |  |  | 5 |  |  | 2 |
Losses |  | (1 | ) |  | (1 | ) |  | (20 | )
AFS fixed income securities |  |  |  |  |  |  |  |  |
Gains |  | 7,741 |  |  | 4,515 |  |  | 1,945 |
Losses |  | (11,411 | ) |  | (312 | ) |  | (392 | )
AFS equity securities |  |  |  |  |  |  |  |  |
Gains |  | 8,108 |  |  | 29,168 |  |  | 36,871 |
Losses |  | (864 | ) |  | (1,347 | ) |  | (704 | )
Short-term investments |  |  |  |  |  |
Gains |  | — |  |  | — |  |  | — |
Losses |  | (13 | ) |  | — |  |  | — |
Other investments |  |  |  |  |  |  |  |  |
Gains |  | 3 |  |  | 162 |  |  | 1 |
Losses |  | (4 | ) |  | (653 | ) |  | — |
Total net realized investment gains |  | $ | 3,562 |  |  | 31,537 |  |  | 37,703 |
Held-to-maturity Securities [Member] |
Investment [Line Items] |
Investments Classified by Contractual Maturity Date [Table Text Block] |
($ in thousands) |  | Carrying Value |  | Fair Value
Due in one year or less |  | $ | 55,505 |  |  | 56,249 |
Due after one year through five years |  | 37,536 |  |  | 39,853 |
Due after five years through 10 years |  | 8,515 |  |  | 9,109 |
Total HTM fixed income securities |  | $ | 101,556 |  |  | 105,211 |
AFS Fixed Income Securities [Member] |
Investment [Line Items] |
Investments Classified by Contractual Maturity Date [Table Text Block] |
($ in thousands) |  | Fair Value
Due in one year or less |  | $ | 374,080 |
Due after one year through five years |  | 2,141,596 |
Due after five years through 10 years |  | 2,090,677 |
Due after 10 years |  | 186,187 |
Total AFS fixed income securities |  | $ | 4,792,540 |

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