Investments - Cost or Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	$ 630,925	$ 489,846
Gross Unrealized Gains	6,079	693
Gross Unrealized Losses	(3,487)	(7,221)
Fair Value	633,517	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	3	10
Fair Value	5,003	25,021
U.S. Government Obligations and Agencies [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	77,076	126,209
Gross Unrealized Gains	618
Gross Unrealized Losses	(63)	(867)
Fair Value	77,631	125,342
Corporate Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	191,342	126,421
Gross Unrealized Gains	2,485	137
Gross Unrealized Losses	(125)	(1,041)
Fair Value	193,702	125,517
Mortgage-Backed and Asset-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	224,423	151,328
Fair Value	226,071	150,160
Mortgage-Backed and Asset-Backed Securities [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	224,423	151,328
Gross Unrealized Gains	1,830	97
Gross Unrealized Losses	(182)	(1,265)
Fair Value	226,071	150,160
Municipal Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	77,135
Gross Unrealized Gains	270
Gross Unrealized Losses	(224)
Fair Value	77,181
Redeemable Preferred Stock [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	9,095	9,665
Gross Unrealized Gains	607	429
Gross Unrealized Losses	(13)	(29)
Fair Value	9,689	10,065
Common Stock [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	11,210	10,991
Gross Unrealized Gains		15
Gross Unrealized Losses	(374)	(244)
Fair Value	10,836	10,762
Mutual Funds [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost or Amortized Cost	35,644	35,221
Gross Unrealized Gains	266	5
Gross Unrealized Losses	(2,506)	(3,774)
Fair Value	$ 33,404	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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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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-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
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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