Segment Information - Income Statement Information (Details) $ in Millions		10 Months Ended	12 Months Ended
	Feb. 26, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) segment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Segment reporting information
Number of operating segments | segment			5
Earned insurance premiums			$ 664.2	$ 22.8	$ 16.3
Net investment income			82.5	131.0	79.7
Net realized and unrealized investment gains (losses)			134.2	30.8	253.2
Realized gain (loss) from the 2019 MediaAlpha Transaction					67.5
Commission revenues			267.6	240.8	249.1
Other revenues			176.6	69.3	47.6
Total revenues			944.8	1,180.7	893.4
Loss and loss adjustment expenses			314.8
Insurance acquisition expenses			186.3	7.0	5.7
Cost of sales			69.3	11.3	48.1
General and administrative expenses			482.9	387.4	328.2
Broker commission expense			80.2	75.3	64.8
Change in fair value of contingent consideration			1.0	(3.3)	2.1
Amortization of other intangible assets			39.8	28.3	21.8
Loss on assets held for sale			28.7
Interest expense			43.8	29.5	17.6
Total expenses			1,246.8	535.5	488.3
Pre-tax income (loss)			(302.0)	645.2	405.1
MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			(380.3)	686.0	180.0
Total revenues		$ 359.2
Total expenses		$ 336.3
HG Global-BAM
Segment reporting information
Earned insurance premiums			26.9	22.8	16.3
Net investment income			17.5	19.5	21.6
Net realized and unrealized investment gains (losses)			(22.9)	23.7	27.1
Realized gain (loss) from the 2019 MediaAlpha Transaction					0.0
Commission revenues			0.0	0.0	0.0
Other revenues			1.5	2.5	1.6
Total revenues			23.0	68.5	66.6
Loss and loss adjustment expenses			0.0
Insurance acquisition expenses			8.3	7.0	5.7
Cost of sales			0.0	0.0	0.0
General and administrative expenses			57.1	56.8	50.9
Broker commission expense			0.0	0.0	0.0
Change in fair value of contingent consideration			0.0	0.0	0.0
Amortization of other intangible assets			0.0	0.0	0.0
Loss on assets held for sale			0.0
Interest expense			0.0	0.0	0.0
Total expenses			65.4	63.8	56.6
Pre-tax income (loss)			(42.4)	4.7	10.0
HG Global-BAM | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			0.0	0.0	0.0
Ark
Segment reporting information
Earned insurance premiums			637.3	0.0	0.0
Net investment income			2.9	0.0	0.0
Net realized and unrealized investment gains (losses)			16.5	0.0	0.0
Commission revenues			0.0
Other revenues			11.8	0.0	0.0
Total revenues			668.5	0.0	0.0
Loss and loss adjustment expenses			314.8	0.0	0.0
Insurance acquisition expenses			178.0	0.0	0.0
Cost of sales			0.0
General and administrative expenses			115.5	0.0	0.0
Broker commission expense			0.0
Change in fair value of contingent consideration			0.0
Amortization of other intangible assets			0.0
Loss on assets held for sale			0.0
Interest expense			7.3	0.0	0.0
Total expenses			615.6	0.0	0.0
Pre-tax income (loss)			52.9
Ark | United Kingdom
Segment reporting information
Earned insurance premiums			459.3
Ark | BERMUDA
Segment reporting information
Earned insurance premiums			178.0
Ark | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			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 (loss) from the 2019 MediaAlpha Transaction					0.0
Commission revenues			258.0	232.5	193.4
Other revenues			72.4	52.6	39.7
Total revenues			330.4	285.1	233.1
Loss and loss adjustment expenses			0.0
Insurance acquisition expenses			0.0	0.0	0.0
Cost of sales			0.0	0.0	0.0
General and administrative expenses			190.1	176.9	132.2
Broker commission expense			80.2	75.3	64.8
Change in fair value of contingent consideration			1.0	(3.3)	2.1
Amortization of other intangible assets			35.2	26.7	19.4
Loss on assets held for sale			28.7	0.0	0.0
Interest expense			23.3	22.1	16.7
Total expenses			358.5	297.7	235.2
Pre-tax income (loss)			$ (28.1)	$ (12.6)	$ (2.1)
Percentage of commission revenue			25.00%	19.00%	17.00%
NSM | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			$ 0.0	$ 0.0	$ 0.0
Kudu
Segment reporting information
Earned insurance premiums			0.0	0.0	0.0
Net investment income			43.9	29.5	14.7
Net realized and unrealized investment gains (losses)			89.9	15.9	6.3
Realized gain (loss) from the 2019 MediaAlpha Transaction					0.0
Commission revenues			0.0	0.0	0.0
Other revenues			0.2	0.3	0.2
Total revenues			134.0	45.7	21.2
Loss and loss adjustment expenses			0.0
Insurance acquisition expenses			0.0	0.0	0.0
Cost of sales			0.0	0.0	0.0
General and administrative expenses			14.5	11.8	10.1
Broker commission expense			0.0	0.0	0.0
Change in fair value of contingent consideration			0.0	0.0	0.0
Amortization of other intangible assets			0.3	0.3	0.2
Loss on assets held for sale			0.0
Interest expense			11.7	6.0	0.1
Total expenses			26.5	18.1	10.4
Pre-tax income (loss)			107.5	27.6	10.8
Kudu | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			0.0	0.0	0.0
MediaAlpha
Segment reporting information
Earned insurance premiums					0.0
Net investment income					0.0
Net realized and unrealized investment gains (losses)					0.0
Realized gain (loss) from the 2019 MediaAlpha Transaction					0.0
Commission revenues			0.0	0.0	48.8
Other revenues					0.0
Total revenues			0.0	0.0	48.8
Insurance acquisition expenses					0.0
Cost of sales			0.0	0.0	40.6
General and administrative expenses			0.0		12.5
Broker commission expense					0.0
Change in fair value of contingent consideration					0.0
Amortization of other intangible assets			0.0	0.0	1.6
Interest expense			0.0	0.0	0.2
Total expenses			0.0	0.0	54.9
Pre-tax income (loss)					(6.1)
MediaAlpha | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha					0.0
Other Operations
Segment reporting information
Earned insurance premiums			0.0	0.0	0.0
Net investment income			18.2	82.0	43.4
Net realized and unrealized investment gains (losses)			50.7	(8.8)	219.8
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			(380.3)	686.0	180.0
Realized gain (loss) from the 2019 MediaAlpha Transaction			0.0	0.0	67.5
Commission revenues			9.6	8.3	6.9
Other revenues			90.7	13.9	6.1
Total revenues			(211.1)	781.4	523.7
Loss and loss adjustment expenses			0.0
Insurance acquisition expenses			0.0	0.0	0.0
Cost of sales			69.3	11.3	7.5
General and administrative expenses			105.7	141.9	122.5
Broker commission expense			0.0	0.0	0.0
Change in fair value of contingent consideration			0.0	0.0	0.0
Amortization of other intangible assets			4.3	1.3	0.6
Loss on assets held for sale			0.0
Interest expense			1.5	1.4	0.6
Total expenses			180.8	155.9	131.2
Pre-tax income (loss)			$ (391.9)	$ 625.5	$ 392.5
MediaAlpha
Segment reporting information
Realized gain (loss) from the 2019 MediaAlpha Transaction	$ 67.5