Investment Securities (Significant Unobservable Inputs) (Details) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / shares
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI		$ 57.4	$ 0.0
MediaAlpha | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 225.0	$ 225.0		$ 180.0
MediaAlpha | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		14.00%		15.00%
MediaAlpha | Measurement Input, Long-term Revenue Growth Rate [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
DavidShield & PassportCard | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 95.0	$ 95.0		$ 90.0
DavidShield & PassportCard | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		23.00%		22.00%
DavidShield & PassportCard | Measurement Input, Long-term Revenue Growth Rate [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
Private Debt Instrument | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 17.5	$ 17.5		$ 23.7
Private Debt Instrument | Minimum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		6.00%		4.00%
Private Debt Instrument | Maximum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		12.00%		9.00%
Kudu Investments | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 315.6	$ 315.6		$ 266.5
Kudu Investments | Minimum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		18.00%		15.00%
Kudu Investments | Minimum | Terminal Multiple | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Cash Flow Exit Multiple	6	6		6
Kudu Investments | Maximum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		23.00%		22.00%
Kudu Investments | Maximum | Terminal Multiple | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Cash Flow Exit Multiple	12	12		12
Elementum Holdings, L.P. | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 55.1	$ 55.1		$ 55.1
Elementum Holdings, L.P. | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		19.00%		20.00%
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
Other | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 15.7	$ 15.7		$ 23.7
Other | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		24.00%
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
Other | Minimum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate				25.00%
Other | Minimum | Measurement Input, Revenue Multiple [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	2	2		2
Other | Maximum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate				32.00%
Other | Maximum | Measurement Input, Revenue Multiple [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	4	4		4
Noblr Inc [Member] | Standard Poors NR Rating | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 8.7	$ 8.7		$ 5.0
Noblr Inc [Member] | Recent transaction | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price | $ / shares	$ 2.17	$ 2.17		$ 2.17
Compare.com | Standard Poors NR Rating | Estimated Net Realizable Value
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 2.5	$ 2.5		$ 2.5
Compare.com | Estimated Net Realizable Value | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	2.5	2.5		2.5
Zillion Insurance Services [Member] | Standard Poors NR Rating | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	5.0	5.0		2.5
Zillion Insurance Services [Member] | Recent transaction | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	5.0	5.0		$ 2.5
Zillion Insurance Services [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI	2.5
Kudu
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI		$ 57.4
Passport/DavidShield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI	$ 15.0