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Investment Securities - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment income:
Total investment income	$ 132.2	$ 81.0	$ 62.0
Third-party investment expenses	(1.2)	(1.3)	(3.0)
Net investment income	131.0	79.7	59.0
Fixed maturity investments
Investment income:
Total investment income	29.0	32.4	35.1
Short-term investments
Investment income:
Total investment income	1.1	5.0	8.0
Common equity securities
Investment income:
Total investment income	6.6	13.5	15.1
Other long-term investments
Investment income:
Total investment income	35.6	22.1	3.8
MediaAlpha
Investment income:
Total investment income	$ 59.9	$ 8.0	$ 0.0

X

- 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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
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Amount of expenses related to the generation of investment income.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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

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