Investments - Summarized Fair Value and Gross Unrealized Losses on Securities Available for Sale (Detail) $ in Thousands	Sep. 30, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	65	174
Less than 12 months, Fair value	$ 93,838	$ 359,017
Less than 12 months, Unrealized losses	$ (676)	$ (3,143)
12 months or longer, Number of issues \| Security	16	17
12 months or longer, Fair value	$ 27,714	$ 30,080
12 months or longer, Unrealized losses	(2,811)	$ (4,078)
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
12 months or longer, Fair value	$ 12,000
U.S. Government Obligations and Agencies [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	1	10
Less than 12 months, Fair value	$ 922	$ 121,912
Less than 12 months, Unrealized losses	$ (6)	$ (690)
12 months or longer, Number of issues \| Security	2	2
12 months or longer, Fair value	$ 3,518	$ 3,429
12 months or longer, Unrealized losses	$ (57)	$ (177)
Corporate Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	18	101
Less than 12 months, Fair value	$ 13,627	$ 90,717
Less than 12 months, Unrealized losses	$ (23)	$ (927)
12 months or longer, Number of issues \| Security	6	6
12 months or longer, Fair value	$ 5,362	$ 4,789
12 months or longer, Unrealized losses	$ (102)	$ (114)
Mortgage-Backed and Asset-Backed Securities [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	12	51
Less than 12 months, Fair value	$ 25,089	$ 118,743
Less than 12 months, Unrealized losses	$ (96)	$ (974)
12 months or longer, Number of issues \| Security	4	6
12 months or longer, Fair value	$ 6,858	$ 13,902
12 months or longer, Unrealized losses	$ (86)	$ (291)
Municipal Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	25
Less than 12 months, Fair value	$ 32,976
Less than 12 months, Unrealized losses	$ (224)
Redeemable Preferred Stock [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	5	5
Less than 12 months, Fair value	$ 479	$ 764
Less than 12 months, Unrealized losses	$ (13)	$ (29)
Common Stock [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	3	3
Less than 12 months, Fair value	$ 10,754	$ 8,690
Less than 12 months, Unrealized losses	$ (265)	$ (148)
12 months or longer, Number of issues \| Security	2	2
12 months or longer, Fair value	$ 81	$ 93
12 months or longer, Unrealized losses	$ (109)	$ (96)
Mutual Funds [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	1	3
Less than 12 months, Fair value	$ 9,991	$ 13,192
Less than 12 months, Unrealized losses	$ (49)	$ (374)
12 months or longer, Number of issues \| Security	2	1
12 months or longer, Fair value	$ 11,895	$ 7,867
12 months or longer, Unrealized losses	$ (2,457)	$ (3,400)
Other [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security		1
Less than 12 months, Fair value		$ 4,999
Less than 12 months, Unrealized losses		$ (1)

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

+ References

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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