Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment reporting information
Percentage of par value of policy reinsured	15.00%								15.00%
Earned insurance premiums									$ 10.4	$ 13.4	$ 12.0
Net investment income									56.0	32.1	10.9
Net realized and unrealized investment gains									133.3	(27.4)	260.5
Advertising & commission revenues									167.0	118.3	107.4
Other revenues									7.1	21.3	49.2
Total revenues		$ 87.5	$ 83.5	$ 88.8	$ (5.5)	$ 56.8	$ 48.4	$ 58.0	373.8	157.7	440.0
Loss and loss adjustment expenses									1.1	8.0	8.2
Insurance acquisition expenses									4.1	5.6	6.3
Other underwriting expenses									0.4	0.4	0.4
Cost of sales									139.4	102.0	93.6
General and administrative expenses									218.7	186.0	200.7
Interest expense									2.3	3.0	1.6
Total expenses		79.1	85.7	92.4	69.0	70.6	74.1	91.3	366.0	305.0	310.8
Pre-tax (loss) income from continuing operations	$ 5.2	$ 8.4	$ (2.2)	$ (3.6)	$ (74.5)	$ (13.8)	$ (25.7)	$ (33.3)	7.8	(147.3)	129.2
HG Global BAM
Segment reporting information
Advertising & commission revenues									0.0	0.0	0.0
Total revenues									23.3		10.7
Loss and loss adjustment expenses									0.0	0.0	0.0
Cost of sales									0.0	0.0	0.0
Interest expense									0.0	0.0	0.0
Total expenses									47.3	43.4	40.1
Pre-tax (loss) income from continuing operations									(24.0)	(26.7)	(29.4)
MediaAlpha
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									0.0	0.0	0.0
Advertising & commission revenues									163.2	116.5	105.5
Other revenues									0.0	0.0	0.0
Total revenues									163.2	116.5	105.5
Loss and loss adjustment expenses									0.0	0.0	0.0
Insurance acquisition expenses									0.0	0.0	0.0
Other underwriting expenses									0.0	0.0	0.0
Cost of sales									135.9	97.8	90.7
General and administrative expenses									26.7	21.9	16.4
Interest expense									1.0	0.9	0.4
Total expenses									163.6	120.6	107.5
Pre-tax (loss) income from continuing operations									$ (0.4)	$ (4.1)	$ (2.0)
Percentage of Advertising Revenue									27.00%	24.00%	52.00%
Other Segments
Segment reporting information
Earned insurance premiums									$ 1.0	$ 7.5	$ 8.7
Net investment income									43.7	23.1	4.8
Net realized and unrealized investment gains									132.7	(28.1)	259.9
Advertising & commission revenues									3.8	1.8	1.9
Other revenues									6.1	20.2	48.5
Total revenues									187.3	24.5	323.8
Loss and loss adjustment expenses									1.1	8.0	8.2
Insurance acquisition expenses									0.1	2.2	3.4
Other underwriting expenses									0.0	0.0	0.0
Cost of sales									3.5	4.2	2.9
General and administrative expenses									149.1	124.5	147.5
Interest expense									1.3	2.1	1.2
Total expenses									155.1	141.0	163.2
Pre-tax (loss) income from continuing operations									32.2	(116.5)	160.6
HG Global BAM
Segment reporting information
Earned insurance premiums									9.4	5.9	3.3
Net investment income									12.3	9.0	6.1
Net realized and unrealized investment gains									0.6	0.7	0.6
Other revenues									1.0	1.1	0.7
Total revenues									23.3	16.7	10.7
Insurance acquisition expenses									4.0	3.4	2.9
Other underwriting expenses									0.4	0.4	0.4
General and administrative expenses									42.9	39.6	36.8
Total expenses									$ 47.3	$ 43.4	40.1
Symetra | Other Segments
Segment reporting information
Net realized and unrealized investment gains											$ 258.8