Investments - Gross Unrealized Gains and Losses and Cost or Amortized Cost and Fair Value of Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	$ 475,998	$ 489,871
Available-for-Sale, Gross Unrealized Gains	8,396	8,156
Available-for-Sale, Gross Unrealized Losses	(4,704)	(5,567)
Available-for-Sale, Fair Value	479,690	492,460
Other Investments [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	6,000	10,000
Available-for-Sale, Gross Unrealized Gains	2,956	3,330
Available-for-Sale, Fair Value	8,956	13,330
Total Fixed Maturity [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	467,989	479,871
Available-for-Sale, Gross Unrealized Gains	5,405	4,793
Available-for-Sale, Gross Unrealized Losses	(4,704)	(5,567)
Available-for-Sale, Fair Value	468,690	479,097
States and Political Subdivisions [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	235,741	231,168
Available-for-Sale, Gross Unrealized Gains	4,770	4,340
Available-for-Sale, Gross Unrealized Losses	(2,794)	(3,215)
Available-for-Sale, Fair Value	237,717	232,293
Corporate Bonds [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	160,612	182,350
Available-for-Sale, Gross Unrealized Gains	584	436
Available-for-Sale, Gross Unrealized Losses	(165)	(271)
Available-for-Sale, Fair Value	161,031	182,515
U.S. Agency-Based Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	10,082	10,428
Available-for-Sale, Gross Unrealized Gains	12	17
Available-for-Sale, Gross Unrealized Losses	(911)	(1,103)
Available-for-Sale, Fair Value	9,183	9,342
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	61,554	55,925
Available-for-Sale, Gross Unrealized Gains	39
Available-for-Sale, Gross Unrealized Losses	(834)	(978)
Available-for-Sale, Fair Value	60,759	54,947
Equity Securities [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	2,009
Available-for-Sale, Gross Unrealized Gains	35	33
Available-for-Sale, Fair Value	$ 2,044	$ 33

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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