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Investment Securities (Significant Unobservable Inputs) (Details) - NR $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares
Kudu Investments | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 21.0
MediaAlpha | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 210.0	$ 180.0
MediaAlpha | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	15.00%	15.00%
MediaAlpha | Long-term revenue growth
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%
DavidShield & PassportCard | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 80.0	$ 90.0
DavidShield & PassportCard | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	25.00%	22.00%
DavidShield & PassportCard | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%
Equity Securities, FV-NI, Measurement Input	1	1
Private Debt Instrument | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 25.8	$ 23.7
Private Debt Instrument | Minimum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	7.00%	4.00%
Private Debt Instrument | Maximum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	15.00%	9.00%
Kudu Investments | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 262.7	$ 266.5
Kudu Investments | Minimum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	18.00%	15.00%
Kudu Investments | Minimum | Long-term revenue growth
Quantitative information for Level 3 Fair Value Measurements Assets
Measurement input	6	6
Kudu Investments | Maximum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	24.00%	22.00%
Kudu Investments | Maximum | Long-term revenue growth
Quantitative information for Level 3 Fair Value Measurements Assets
Measurement input	12	12
Elementum Holdings, L.P. | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 55.1	$ 55.1
Elementum Holdings, L.P. | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	20.00%	20.00%
Terminal Revenue Growth Rate	4.00%	4.00%
Other | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 13.6	$ 23.7
Other | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	25.00%
Terminal Revenue Growth Rate	4.00%	4.00%
Other | Minimum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		25.00%
Other | Minimum | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	2	2
Other | Maximum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		32.00%
Other | Maximum | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	4	4
Noblr Inc [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 8.7	$ 5.0
Noblr Inc [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price | $ / shares	$ 2.17	$ 2.17
Compare.com | Estimated Net Realizable Value
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 2.5	$ 2.5
Compare.com | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input		3
Compare.com | Estimated Net Realizable Value
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	2.5	$ 2.5
Zillion Insurance Services [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	2.5	2.5
Zillion Insurance Services [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 2.5	$ 2.5

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