Current Liquidity and Statutory Capital and Surplus - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Current Liquidity And Statutory Capital And Surplus [Line Items]
Long-term debt obligations	$ 70.0
Statutory capital and surplus balance	$ 66.1	$ 58.9
Ratio of net premiums to statutory capital and surplus	4.27%
Increase in statutory capital and surplus	$ 7.2
Reduction in premiums written	$ 17.0
Percentage of reduction in premiums written	6.00%
Minimum
Current Liquidity And Statutory Capital And Surplus [Line Items]
Ratio of net premiums to statutory capital and surplus	3.00%
Long-term debt matures on 2037
Current Liquidity And Statutory Capital And Surplus [Line Items]
Long-term debt obligations	$ 40.0
Long-term debt matures on 2025
Current Liquidity And Statutory Capital And Surplus [Line Items]
Long-term debt obligations	$ 30.0

Current liquidity and statutory capital and surplus line items.

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- Definition

Increase decrease in premiums written.

+ References

No definition available.

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- Definition

Increase in statutory capital and surplus.

+ References

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- Definition

Percentage of increase decrease in premiums written.

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- Definition

Statutory accounting practices statutory capital and surplus current percentage.

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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

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- Definition

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

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