Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment reporting information
Earned insurance premiums	$ 2.4	$ 3.4	$ 7.6	$ 10.2
Net investment income	12.2	9.6	39.7	18.2
Net investment income (loss) - BAM Surplus Note interest	0.0	0.0	0.0	0.0
Net realized and unrealized investment gains	32.5	10.9	102.5	27.2
Advertising and commission revenues	38.8	28.2	103.9	89.6
Other revenue	1.6	4.7	6.1	18.0
Total revenues	87.5	56.8	259.8	163.2
Loss and loss adjustment expenses	0.0	2.2	1.1	6.8
Insurance acquisition expenses	0.9	1.3	3.1	4.4
Other underwriting expenses	0.1	0.2	0.3	0.4
Cost of sales	33.1	24.0	88.7	76.9
General and administrative expenses	44.1	42.4	162.2	144.9
Interest expense	0.9	0.5	1.8	2.6
Total expenses	79.1	70.6	257.2	236.0
Pre-tax income (loss)	8.4	(13.8)	2.6	(72.8)
HG Global
Segment reporting information
Earned insurance premiums	1.8	1.2	5.0	3.1
Net investment income	1.0	0.6	2.4	1.6
Net investment income (loss) - BAM Surplus Note interest	4.8	4.5	14.3	13.4
Net realized and unrealized investment gains	0.1	(0.3)	0.4	2.3
Advertising and commission revenues	0.0	0.0	0.0	0.0
Other revenue	0.0	0.0	0.0	0.0
Total revenues	7.7	6.0	22.1	20.4
Loss and loss adjustment expenses		0.0	0.0	0.0
Insurance acquisition expenses	0.4	0.2	1.0	0.6
Other underwriting expenses	0.0	0.0	0.0	0.0
Cost of sales	0.0	0.0	0.0	0.0
General and administrative expenses	0.3	0.6	0.8	1.4
Interest expense	0.0	0.0	0.0	0.0
Total expenses	0.7	0.8	1.8	2.0
Pre-tax income (loss)	7.0	5.2	20.3	18.4
BAM
Segment reporting information
Earned insurance premiums	0.6	0.3	1.6	1.0
Net investment income	2.3	1.7	6.5	5.1
Net investment income (loss) - BAM Surplus Note interest	(4.8)	(4.5)	(14.3)	(13.4)
Net realized and unrealized investment gains	0.7	(1.6)	2.8	6.5
Advertising and commission revenues	0.0	0.0	0.0	0.0
Other revenue	0.2	0.4	0.8	0.8
Total revenues	(1.0)	(3.7)	(2.6)	0.0
Loss and loss adjustment expenses		0.0	0.0	0.0
Insurance acquisition expenses	0.5	0.6	2.0	1.9
Other underwriting expenses	0.1	0.1	0.3	0.3
Cost of sales	0.0	0.0	0.0	0.0
General and administrative expenses	10.3	9.3	30.7	28.1
Interest expense	0.0	0.0	0.0	0.0
Total expenses	10.9	10.0	33.0	30.3
Pre-tax income (loss)	(11.9)	(13.7)	(35.6)	(30.3)
MediaAlpha
Segment reporting information
Earned insurance premiums	0.0	0.0	0.0	0.0
Net investment income	0.0	0.0	0.0	0.0
Net investment income (loss) - BAM Surplus Note interest	0.0	0.0	0.0	0.0
Net realized and unrealized investment gains	0.0	0.0	0.0	0.0
Advertising and commission revenues	37.9	27.6	101.2	88.4
Other revenue	0.0	0.0	0.0	0.0
Total revenues	37.9	27.6	101.2	88.4
Loss and loss adjustment expenses			0.0	0.0
Insurance acquisition expenses	0.0	0.0	0.0	0.0
Other underwriting expenses	0.0	0.0	0.0	0.0
Cost of sales	32.2	23.0	86.0	74.0
General and administrative expenses	6.1	5.7	17.9	16.3
Interest expense	0.1	0.2	0.6	0.7
Total expenses	38.4	28.9	104.5	91.0
Pre-tax income (loss)	(0.5)	(1.3)	(3.3)	(2.6)
Other Operations
Segment reporting information
Earned insurance premiums	0.0	1.9	1.0	6.1
Net investment income	8.9	7.3	30.8	11.5
Net investment income (loss) - BAM Surplus Note interest	0.0	0.0	0.0	0.0
Net realized and unrealized investment gains	31.7	12.8	99.3	18.4
Advertising and commission revenues	0.9	0.6	2.7	1.2
Other revenue	1.4	4.3	5.3	17.2
Total revenues	42.9	26.9	139.1	54.4
Loss and loss adjustment expenses		2.2	1.1	6.8
Insurance acquisition expenses	0.0	0.5	0.1	1.9
Other underwriting expenses	0.0	0.1	0.0	0.1
Cost of sales	0.9	1.0	2.7	2.9
General and administrative expenses	27.4	26.8	112.8	99.1
Interest expense	0.8	0.3	1.2	1.9
Total expenses	29.1	30.9	117.9	112.7
Pre-tax income (loss)	$ 13.8	$ (4.0)	$ 21.2	$ (58.3)