Segment Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Mar. 31, 2018
Segment reporting information
Net investment income		$ 16.0	$ 19.7
Net realized and unrealized investment gains (losses)		245.6	(53.7)
Total revenues		433.6	42.1
Amortization		6.6
Total expenses		151.9	108.1
Pre-tax income (loss)		281.7	(66.0)
HG Global-BAM
Segment reporting information
Earned insurance premiums		4.2	3.0
Net investment income		5.3	3.7
Net realized and unrealized investment gains (losses)		11.8	(7.9)
Other revenue		0.6	0.2
Insurance acquisition expenses		1.3	1.4
General and administrative expenses		14.4	11.9
NSM Holding Co LLC
Segment reporting information
Commission revenues		43.3	0.0
Other revenue		6.0	0.0
Total revenues		49.3	0.0
General and administrative expenses		25.1	0.0
Broker commission expense		15.7	0.0
Change in fair value of contingent consideration earnout liabilities		1.3	0.0
Amortization		5.0	0.0
Interest expense		3.7	0.0
Total expenses		50.8	0.0
MediaAlpha
Segment reporting information
Commission revenues		48.8	70.1
Other revenue		0.0	1.6
Cost of sales		40.6	57.4
General and administrative expenses		12.5	11.2
Amortization		1.6	2.9
Interest expense		0.2	$ 0.4
Percentage of advertising revenue			31.00%
Other Segment
Segment reporting information
Earned insurance premiums		0.0	$ 0.0
Net investment income		10.7	16.0
Net realized and unrealized investment gains (losses)		119.1	(45.8)
Commission revenues		1.3	0.9
Other revenue		0.3	0.3
Insurance acquisition expenses		0.0	0.0
Cost of sales		1.1	0.7
General and administrative expenses		29.4	22.0
Amortization		0.0	0.0
Interest expense		0.0	0.2
Total
Segment reporting information
Earned insurance premiums		4.2	3.0
Net investment income		16.0	19.7
Net realized and unrealized investment gains (losses)		130.9	(53.7)
Commission revenues		93.4	71.0
Other revenue		6.9	2.1
Total revenues		433.6	42.1
Insurance acquisition expenses		1.3	1.4
Cost of sales		41.7	58.1
General and administrative expenses		81.4	45.1
Broker commission expense		15.7
Change in fair value of contingent consideration earnout liabilities		1.3
Amortization			2.9
Interest expense		3.9	0.6
Total expenses		151.9	108.1
Pre-tax income (loss)		281.7	(66.0)
HG Global-BAM | HG Global-BAM
Segment reporting information
Commission revenues		0.0	0.0
Total revenues		21.9	(1.0)
Cost of sales		0.0	0.0
Broker commission expense		0.0
Change in fair value of contingent consideration earnout liabilities		0.0
Amortization		0.0
Interest expense		0.0	0.0
Total expenses		15.7	13.3
Pre-tax income (loss)		6.2	(14.3)
NSM Holding Co LLC | NSM Holding Co LLC
Segment reporting information
Earned insurance premiums		0.0
Net investment income		0.0
Net realized and unrealized investment gains (losses)		0.0
Total revenues		49.3
Insurance acquisition expenses		0.0
Cost of sales		0.0
Pre-tax income (loss)		(1.5)
MediaAlpha | MediaAlpha
Segment reporting information
Earned insurance premiums			0.0
Net investment income			0.0
Net realized and unrealized investment gains (losses)			0.0
Total revenues	$ 33.5	48.8	71.7
Broker commission expense		0.0
Change in fair value of contingent consideration earnout liabilities		0.0
Total expenses		54.9	71.9
Pre-tax income (loss)		(6.1)	(0.2)
Other Operations | Other Segment
Segment reporting information
Total revenues		313.6	(28.6)
Broker commission expense		0.0
Change in fair value of contingent consideration earnout liabilities		0.0
Total expenses		30.5	22.9
Pre-tax income (loss)		283.1	$ (51.5)
MediaAlpha | HG Global-BAM
Segment reporting information
Net realized and unrealized investment gains (losses)		0.0
MediaAlpha | Total
Segment reporting information
Net realized and unrealized investment gains (losses)		182.2
MediaAlpha | NSM Holding Co LLC | NSM Holding Co LLC
Segment reporting information
Net realized and unrealized investment gains (losses)		$ 0.0