Amount, before 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.

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.1-5)
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Amount of expenses related to the generation of investment income.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
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-Subparagraph (SX 210.7-04(2))
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Investments - Investment Income (Expense) Comprised Primarily of Interest and Dividends (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Investment Income [Line Items]
Total investment income									$ 15,655	$ 11,746	$ 7,440
Less: Investment expenses									(2,195)	(2,206)	(2,285)
Net investment (expense) income	$ 4,448	$ 3,085	$ 3,223	$ 2,704	$ 3,489	$ 2,304	$ 2,142	$ 1,605	13,460	9,540	5,155
Fixed Maturities [Member]
Net Investment Income [Line Items]
Investment income									12,375	9,523	5,642
Equity Securities [Member]
Net Investment Income [Line Items]
Investment income									1,799	1,414	1,143
Short-term Investments [Member]
Net Investment Income [Line Items]
Investment income									22	75	246
Other [Member]
Net Investment Income [Line Items]
Investment income									$ 1,459	$ 734	$ 409