Investments - Cost or Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	$ 650,575	$ 489,846
Gross Unrealized Gains	1,201	693
Gross Unrealized Losses	(11,610)	(7,221)
Fair Value	640,166	483,318
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	5,000	25,011
Gross Unrealized Gains	2	10
Fair Value	5,002	25,021
U.S. Government Obligations and Agencies [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	74,937	126,209
Gross Unrealized Losses	(670)	(867)
Fair Value	74,267	125,342
Corporate Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	192,328	126,421
Gross Unrealized Gains	402	137
Gross Unrealized Losses	(1,300)	(1,041)
Fair Value	191,430	125,517
Mortgage-Backed and Asset-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	216,679	151,328
Fair Value	214,776	150,160
Mortgage-Backed and Asset-Backed Securities [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	216,679	151,328
Gross Unrealized Gains	135	97
Gross Unrealized Losses	(2,038)	(1,265)
Fair Value	214,776	150,160
Municipal Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	94,794
Gross Unrealized Gains	130
Gross Unrealized Losses	(3,727)
Fair Value	91,197
Redeemable Preferred Stock [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	12,723	9,665
Gross Unrealized Gains	125	429
Gross Unrealized Losses	(157)	(29)
Fair Value	12,691	10,065
Common Stock [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	214	10,991
Gross Unrealized Gains		15
Gross Unrealized Losses	(121)	(244)
Fair Value	93	10,762
Mutual Funds [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	53,900	35,221
Gross Unrealized Gains	407	5
Gross Unrealized Losses	(3,597)	(3,774)
Fair Value	$ 50,710	31,452
Other [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost		5,000
Gross Unrealized Losses		(1)
Fair Value		$ 4,999

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

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
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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