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Significant Accounting Policies (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2017 USD ($) Payment | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Home office and equipment [Abstract] |  |  |  |
Accumulated depreciation of home office and equipment | $ 33,900,000 | $ 33,900,000 | $ 30,600,000 | $ 26,100,000
Depreciation expense of home office and equipment |  | $ 5,400,000 | 4,600,000 | 3,200,000
Minimum number of payments past due to be in default | Payment |  | 2 |  |
Decrease in premium deficiency reserve |  | $ 0 | 0 | 23,751,000
Maximum age for qualified employees for both medical and dental benefits |  | 65 years |  |
Related party transaction amount |  | $ 0 | $ 0 | $ 0
Discrete tax benefits realized upon adoption of ASU |  | 1,600,000 |  |
Accumulated other comprehensive loss |  |  |  |
Home office and equipment [Abstract] |  |  |  |
Cumulative effect to reclassify certain tax effects from accumulated other comprehensive loss | (10,400,000) | (10,422,000) |  |
Retained earnings (deficit) |  |  |  |
Home office and equipment [Abstract] |  |  |  |
Cumulative effect to reclassify certain tax effects from accumulated other comprehensive loss | $ 10,400,000 | $ 10,422,000 |  |
Minimum |  |  |  |
Home office and equipment [Abstract] |  |  |  |
Estimated useful life |  | 3 years |  |
Award vesting period |  | 1 year |  |
Maximum |  |  |  |
Home office and equipment [Abstract] |  |  |  |
Estimated useful life |  | 45 years |  |
Award vesting period |  | 3 years |  |

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- Definition Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount + References No definition available. + Details
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- Definition Increase (decrease) in the present value of expected future paid losses and expenses that exceeded the present value of expected future premium to be collected and already established loss and loss adjustment expense reserves. + References No definition available. + Details
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- Definition The number of payments past due in order for such loans to be considered in default. + References No definition available. + Details
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- Definition Postemployment Benefits Liability, Maximum Age For Qualified Employees + References No definition available. + Details
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- Definition Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act of 2017. + References No definition available. + Details
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- Definition Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.14) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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