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Debt (Debt Outstanding) (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Debt Instrument [Line Items] |  |
Debt | $ 23.8 | $ 12.7
White Mountains | WTM Bank Facility |  |
Debt Instrument [Line Items] |  |
Debt | 0.0 | 0.0
MediaAlpha |  |
Debt Instrument [Line Items] |  |
Debt | 23.8 | 12.7
MediaAlpha | MediaAlpha Bank Facility |  |
Debt Instrument [Line Items] |  |
Debt instrument at face value | 23.9 | 0.0
Unamortized Debt Issuance Expense | $ (0.1) | 0.0
Effective yield (as a percent) | 5.60% |
MediaAlpha | Previous MediaAlpha Bank Facility |  |
Debt Instrument [Line Items] |  |
Debt instrument at face value | $ 0.0 | 12.9
Unamortized Debt Issuance Expense | 0.0 | $ (0.2)
Effective yield (as a percent) |  | 5.70%
Debt | 0.0 | $ 12.7
Carrying Value | MediaAlpha | MediaAlpha Bank Facility |  |
Debt Instrument [Line Items] |  |
Debt | 23.8 | 0.0
Carrying Value | MediaAlpha | Previous MediaAlpha Bank Facility |  |
Debt Instrument [Line Items] |  |
Debt | $ 0.0 | $ 12.7

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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 + Details
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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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