Investments - Schedule of Amortized Cost and Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	$ 528,139	$ 552,458
Gross Unrealized Gains	99	1,440
Gross Unrealized Losses	13,894	4,433
Fair Value	531,250	567,013
Investments	545,045	570,006
Fair Value	531,250	567,013
Fixed Maturities Excluding Certificate of Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	528,139	552,458
Gross Unrealized Gains	45	1,307
Gross Unrealized Losses	12,643	3,969
Fair Value	515,541	549,796
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	16,906	17,548
Gross Unrealized Gains	54	133
Gross Unrealized Losses	1,251	464
Fair Value	15,709	17,217
U.S. government and agency securities [Member] \| Fixed Maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	46,934	39,445
Gross Unrealized Gains	2	7
Gross Unrealized Losses	1,051	572
Fair Value	45,885	38,880
States, Municipalities and Political Subdivisions [Member] \| Fixed Maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	61,672	76,876
Gross Unrealized Gains		104
Gross Unrealized Losses	1,527	569
Fair Value	60,145	76,411
Special Revenue [Member] \| Fixed Maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	261,799	269,277
Gross Unrealized Gains	10	524
Gross Unrealized Losses	6,316	2,124
Fair Value	255,493	267,677
Industrial and Miscellaneous [Member] \| Fixed Maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	152,884	162,093
Gross Unrealized Gains	27	668
Gross Unrealized Losses	3,560	633
Fair Value	149,351	162,128
Redeemable Preferred Stocks [Member] \| Fixed Maturity [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	4,850	4,767
Gross Unrealized Gains	6	4
Gross Unrealized Losses	189	71
Fair Value	4,667	4,700
Nonredeemable Preferred Stocks [Member] \| Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	13,808	14,450
Gross Unrealized Gains	17	69
Gross Unrealized Losses	654	195
Fair Value	13,171	14,324
Common Stock [Member] \| Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost or Adjusted / Amortized Cost	3,098	3,098
Gross Unrealized Gains	37	64
Gross Unrealized Losses	597	269
Fair Value	$ 2,538	$ 2,893

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(h))
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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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