Investments - Summary of Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Gross investment income (loss)	$ 4,276	$ 3,375	$ 11,299	$ 9,618
Investment expenses	429	640	1,595	1,408
Net investment income, less investment expenses	3,847	2,735	9,704	8,210
Fixed Maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income (loss)	3,020	2,479	8,018	7,640
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income (loss)	547	479	1,252	1,458
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income (loss)	284	441	861	544
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income (loss)	$ 425	$ (24)	$ 1,168	$ (24)

Amount, before investment expense, of income (loss) earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
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-Name Accounting Standards Codification
-Topic 944
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-Section S99
-Paragraph 1
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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(2))
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