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	Jun. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	$ 457,988	$ 386,109
Available-for-Sale, Gross Unrealized Gains	14,652	9,447
Available-for-Sale, Gross Unrealized Losses	(1,061)	(3,286)
Available-for-Sale, Fair Value	471,579	392,270
Total Fixed Maturity [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	447,988	376,109
Available-for-Sale, Gross Unrealized Gains	13,770	7,199
Available-for-Sale, Gross Unrealized Losses	(1,061)	(3,286)
Available-for-Sale, Fair Value	460,697	380,022
Other Investments [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	10,000	10,000
Available-for-Sale, Gross Unrealized Gains	850	2,217
Available-for-Sale, Fair Value	10,850	12,217
States and Political Subdivisions [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	171,931	164,684
Available-for-Sale, Gross Unrealized Gains	9,788	6,942
Available-for-Sale, Gross Unrealized Losses	(70)	(207)
Available-for-Sale, Fair Value	181,649	171,419
Corporate Bonds [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	201,031	202,537
Available-for-Sale, Gross Unrealized Gains	2,590	253
Available-for-Sale, Gross Unrealized Losses	(288)	(1,486)
Available-for-Sale, Fair Value	203,333	201,304
U.S. Agency-Based Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	12,672	8,888
Available-for-Sale, Gross Unrealized Gains	46	4
Available-for-Sale, Gross Unrealized Losses	(703)	(1,593)
Available-for-Sale, Fair Value	12,015	7,299
Equity Securities [Member]
Investment [Line Items]
Available-for-Sale, Gross Unrealized Gains	32	31
Available-for-Sale, Fair Value	32	$ 31
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Investment [Line Items]
Available-for-Sale, Cost or Amortized Cost	62,354
Available-for-Sale, Gross Unrealized Gains	1,346
Available-for-Sale, Fair Value	$ 63,700

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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

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-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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
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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.

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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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