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Debt (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	May 11, 2018	Dec. 31, 2017	Oct. 05, 2017	May 12, 2017	Dec. 12, 2016	Aug. 14, 2013
Debt Instrument
Total debt	$ 164.3	$ 164.3			$ 23.8
Repayments of debt		11.2	$ 364.6
WTM Bank Facility
Debt Instrument
Total commitment under revolving credit facility									$ 425.0
MediaAlpha
Debt Instrument
Total debt	15.0	15.0			23.8
MediaAlpha | MediaAlpha Bank Facility
Debt Instrument
Total debt	15.0	15.0			23.8
Face amount	$ 15.1	$ 15.1			$ 23.9
Effective percentage	6.82%	6.82%			5.60%
Unamortized issuance cost	$ (0.1)	$ (0.1)			$ (0.1)
Total commitment under revolving credit facility						$ 28.4	$ 20.0
NSM Holding Co LLC
Debt Instrument
Total debt	149.3	149.3			0.0
NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total commitment under revolving credit facility				$ 100.0
Revolving Credit Facility | MediaAlpha | MediaAlpha Bank Facility
Debt Instrument
Long-term line of credit	10.0	$ 10.0
Revolving Credit Facility | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total commitment under revolving credit facility				10.0
Borrowings under facility				2.0
Term Loan | MediaAlpha Bank Facility
Debt Instrument
Basis spread on variable rate		1.50%
Term Loan | MediaAlpha | MediaAlpha Bank Facility
Debt Instrument
Face amount	15.1	$ 15.1
Total commitment under revolving credit facility	18.4	18.4
Repayments of debt	0.8	2.8
Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt	147.3	147.3			0.0
Face amount	$ 150.6	$ 150.6			0.0
Effective percentage	7.50%	7.50%
Unamortized issuance cost	$ (3.3)	$ (3.3)			0.0
Long-term line of credit				$ 51.0
Repayments of debt	$ 0.4
Debt, weighted average interest rate, all-in	6.69%	6.69%
Term Loan | NSM Holding Co LLC | Other
Debt Instrument
Total debt	$ 2.0	$ 2.0			0.0
Term Loan | NSM Holding Co LLC | Ageas Bank Facility
Debt Instrument
Long-term line of credit	2.3	$ 2.3
Acquisition date fair value of debt								$ 2.0
Line of Credit | MediaAlpha Bank Facility
Debt Instrument
Basis spread on variable rate		0.25%
Line of Credit | MediaAlpha | MediaAlpha Bank Facility
Debt Instrument
Repayment of lines of credit	4.0	$ 6.0
Line of Credit | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Repayment of lines of credit	$ 2.0
Interest Rate Swap | NSM Holding Co LLC
Debt Instrument
Derivative, fixed interest rate	2.9745%	2.9745%
Derivative, variable interest rate	2.07%	2.07%
Interest Rate Swap | Term Loan | NSM Bank Facility
Debt Instrument
Derivative, variable interest rate	2.07325%	2.07325%
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Derivative, fixed interest rate	2.9745%	2.9745%
Debt, weighted average interest rate, all-in	7.47%	7.47%
Carrying Value | MediaAlpha | MediaAlpha Bank Facility
Debt Instrument
Total debt	$ 15.0	$ 15.0			$ 23.8
Carrying Value | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt	$ 147.3	$ 147.3
London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate	4.25%
London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate	4.75%
Prime Rate | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate	3.25%
Prime Rate | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate	3.75%

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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