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Segment Information (Details) $ in Millions		3 Months Ended								10 Months Ended	12 Months Ended
	Feb. 26, 2019 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) numberOfSegments	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment reporting information
Number of operating segments | numberOfSegments											4
Earned insurance premiums											$ 22.8	$ 16.3	$ 13.9
Net investment income											131.0	79.7	59.0
Net realized and unrealized investment gains (losses)											30.8	253.2	(108.3)
Net realized and unrealized investment gains from MediaAlpha											716.8	433.2	(108.3)
Realized gain from the 2019 MediaAlpha Transaction												67.5
Commission revenues											240.8	249.1	389.2
Other revenues											69.3	47.6	15.3
Total revenues		$ 520.8	$ 459.5	$ 259.6	$ (59.2)	$ 175.3	$ 155.5	$ 129.0	$ 433.6		1,180.7	893.4	369.1
Insurance acquisition expenses											7.0	5.7	5.3
Other underwriting expenses											0.4	0.4	0.4
Cost of sales											11.3	48.1	248.7
General and administrative expenses											387.0	327.8	233.5
Broker commission expense											75.3	64.8	28.4
Change in fair value of contingent consideration earnout liabilities											(3.3)	2.1	2.7
Amortization of other intangible assets											28.3	21.8	18.8
Interest expense											29.5	17.6	9.5
Total expenses		163.5	138.3	126.9	106.8	118.8	104.4	113.2	151.9		535.5	488.3	547.3
Pre-tax income (loss) from continuing operations		$ 357.3	$ 321.2	$ 132.7	$ (166.0)	$ 56.5	$ 51.1	$ 15.8	$ 281.7		645.2	405.1	(178.2)
MediaAlpha
Segment reporting information
Net investment income											95.0	14.8	3.7
Net realized and unrealized investment gains from MediaAlpha											686.0	180.0	0.0
Total revenues										$ 359.2
HG Global-BAM
Segment reporting information
Earned insurance premiums											22.8	16.3	13.9
Net investment income											19.5	21.6	16.7
Net realized and unrealized investment gains (losses)											23.7	27.1	(7.5)
Realized gain from the 2019 MediaAlpha Transaction												0.0
Commission revenues											0.0	0.0	0.0
Other revenues											2.5	1.6	1.2
Total revenues											68.5	66.6	24.3
Insurance acquisition expenses											7.0	5.7	5.3
Other underwriting expenses											0.4	0.4	0.4
Cost of sales											0.0	0.0	0.0
General and administrative expenses											56.4	50.5	48.0
Broker commission expense											0.0	0.0	0.0
Change in fair value of contingent consideration earnout liabilities											0.0	0.0	0.0
Amortization of other intangible assets											0.0	0.0	0.0
Interest expense											0.0	0.0	0.0
Total expenses											63.8	56.6	53.7
Pre-tax income (loss) from continuing operations											4.7	10.0	(29.4)
HG Global-BAM | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains from MediaAlpha											0.0	0.0
NSM
Segment reporting information
Earned insurance premiums											0.0	0.0	0.0
Net investment income											0.0	0.0	0.0
Net realized and unrealized investment gains (losses)											0.0	0.0	0.0
Realized gain from the 2019 MediaAlpha Transaction												0.0
Commission revenues											232.5	193.4	89.6
Other revenues											52.6	39.7	12.0
Total revenues											285.1	233.1	101.6
Insurance acquisition expenses											0.0	0.0	0.0
Other underwriting expenses											0.0	0.0	0.0
Cost of sales											0.0	0.0	0.0
General and administrative expenses											176.9	132.2	59.4
Broker commission expense											75.3	64.8	28.4
Change in fair value of contingent consideration earnout liabilities											(3.3)	2.1	2.7
Amortization of other intangible assets											26.7	19.4	8.3
Interest expense											22.1	16.7	8.0
Total expenses											297.7	235.2	106.8
Pre-tax income (loss) from continuing operations											$ (12.6)	$ (2.1)	$ (5.2)
Percentage of commission revenue											19.00%	17.00%	33.00%
Percentage of advertising revenue													29.00%
NSM | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains from MediaAlpha											$ 0.0	$ 0.0
Kudu
Segment reporting information
Earned insurance premiums											0.0	0.0
Net investment income											29.5	14.7	$ 0.0
Net realized and unrealized investment gains (losses)											15.9	6.3	0.0
Realized gain from the 2019 MediaAlpha Transaction
Commission revenues											0.0	0.0
Other revenues											0.3	0.2	0.0
Total revenues											45.7	21.2	0.0
Insurance acquisition expenses											0.0	0.0
Other underwriting expenses											0.0	0.0
Cost of sales											0.0	0.0
General and administrative expenses											11.8	10.1	0.0
Broker commission expense											0.0	0.0
Change in fair value of contingent consideration earnout liabilities											0.0	0.0
Amortization of other intangible assets											0.3	0.2	0.0
Interest expense											6.0	0.1	0.0
Total expenses											18.1	10.4	0.0
Pre-tax income (loss) from continuing operations											27.6	10.8
Kudu | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains from MediaAlpha											0.0	0.0
MediaAlpha
Segment reporting information
Earned insurance premiums												0.0	0.0
Net investment income												0.0	0.0
Net realized and unrealized investment gains (losses)												0.0	0.0
Realized gain from the 2019 MediaAlpha Transaction												0.0
Commission revenues											0.0	48.8	295.5
Other revenues											0.0	0.0	1.6
Total revenues											0.0	48.8	297.1
Insurance acquisition expenses												0.0	0.0
Other underwriting expenses												0.0	0.0
Cost of sales											0.0	40.6	245.0
General and administrative expenses											0.0	12.5	31.7
Broker commission expense												0.0	0.0
Change in fair value of contingent consideration earnout liabilities												0.0	0.0
Amortization of other intangible assets											0.0	1.6	10.3
Interest expense											0.0	0.2	1.2
Total expenses											0.0	54.9	288.2
Pre-tax income (loss) from continuing operations												(6.1)	8.9
MediaAlpha | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains from MediaAlpha												0.0
Other Operations
Segment reporting information
Earned insurance premiums											0.0	0.0	0.0
Net investment income											82.0	43.4	42.3
Net realized and unrealized investment gains (losses)											(8.8)	219.8	(100.8)
Net realized and unrealized investment gains from MediaAlpha													0.0
Realized gain from the 2019 MediaAlpha Transaction											0.0	67.5	0.0
Commission revenues											8.3	6.9	4.1
Other revenues											13.9	6.1	0.5
Total revenues											781.4	523.7	(53.9)
Insurance acquisition expenses											0.0	0.0	0.0
Other underwriting expenses											0.0	0.0	0.0
Cost of sales											11.3	7.5	3.7
General and administrative expenses											141.9	122.5	94.4
Broker commission expense											0.0	0.0	0.0
Change in fair value of contingent consideration earnout liabilities											0.0	0.0	0.0
Amortization of other intangible assets											1.3	0.6	0.2
Interest expense											1.4	0.6	0.3
Total expenses											155.9	131.2	98.6
Pre-tax income (loss) from continuing operations											625.5	392.5	$ (152.5)
Other Operations | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains from MediaAlpha											$ 686.0	$ 180.0
MediaAlpha
Segment reporting information
Realized gain from the 2019 MediaAlpha Transaction	$ 67.5

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