Fair Value of Financial Instruments - Schedule of Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	$ 616,084	$ 509,649
Investments reported at NAV	28,990	3,910
Total investments	645,074	528,593
Equity securities		15,034
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	366	4,861
Total investments	366	19,895
Equity securities		15,034
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	615,718	504,788
Total investments	615,718	504,788
U.S. government and agency securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	62,989	48,041
U.S. government and agency securities [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	366	354
U.S. government and agency securities [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	62,623	47,687
States, Municipalities and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	81,211	59,289
States, Municipalities and Political Subdivisions [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	81,211	59,289
Special Revenue [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	269,519	245,355
Special Revenue [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	269,519	245,355
Industrial and Miscellaneous [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	202,365	152,457
Industrial and Miscellaneous [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value	$ 202,365	152,457
Redeemable Preferred Stocks [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value		4,507
Redeemable Preferred Stocks [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturity securities, available-for-sale, Fair Value		4,507
Common Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities		2,264
Common Stock [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities		2,264
Nonredeemable Preferred Stocks [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities		12,770
Nonredeemable Preferred Stocks [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities		$ 12,770

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
-Section 45
-Paragraph 1
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
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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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Sum of the carrying amounts as of the balance sheet date of all investments.

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