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Investment Securities - Net Investment Income (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Investment income: |  |  |
Total investment income | $ 126.5 | $ 84.8 | $ 132.2
Third-party investment expenses | (2.1) | (2.3) | (1.2)
Net investment income, pre-tax | 124.4 | 82.5 | 131.0
Fixed maturity investments |  |  |
Investment income: |  |  |
Total investment income | 41.4 | 28.8 | 29.0
Short-term investments |  |  |
Investment income: |  |  |
Total investment income | 16.4 | 0.6 | 1.1
Common equity securities |  |  |
Investment income: |  |  |
Total investment income | 1.6 | 0.1 | 6.6
MediaAlpha |  |  |
Investment income: |  |  |
Total investment income | 0.0 | 0.0 | 59.9
Other long-term investments |  |  |
Investment income: |  |  |
Total investment income | 68.1 | 56.3 | 35.6
Amount attributable to TPC Providers |  |  |
Investment income: |  |  |
Amount attributable to TPC Providers | $ (1.0) | $ (1.0) | $ 0.0

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- Definition Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.1-5) -URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 + Details
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- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 + Details
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