Investments - Summarized Fair Value and Gross Unrealized Losses on Securities Available for Sale (Detail) $ in Thousands	Dec. 31, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	174	108
Less than 12 months, Fair value	$ 359,017	$ 183,191
Less than 12 months, Unrealized losses	$ (3,143)	$ (702)
12 months or longer, Number of issues \| Security	17	24
12 months or longer, Fair value	$ 30,080	$ 74,973
12 months or longer, Unrealized losses	$ (4,078)	$ (2,799)
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security		2
Less than 12 months, Fair value		$ 37,490
Less than 12 months, Unrealized losses		$ (10)
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	10	3
Less than 12 months, Fair value	$ 121,912	$ 27,341
Less than 12 months, Unrealized losses	$ (690)	$ (55)
12 months or longer, Number of issues \| Security	2	4
12 months or longer, Fair value	$ 3,429	$ 34,050
12 months or longer, Unrealized losses	$ (177)	$ (572)
Corporate Bonds [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	101	67
Less than 12 months, Fair value	$ 90,717	$ 58,271
Less than 12 months, Unrealized losses	$ (927)	$ (238)
12 months or longer, Number of issues \| Security	6	12
12 months or longer, Fair value	$ 4,789	$ 15,105
12 months or longer, Unrealized losses	$ (114)	$ (126)
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	51	20
Less than 12 months, Fair value	$ 118,743	$ 48,335
Less than 12 months, Unrealized losses	$ (974)	$ (273)
12 months or longer, Number of issues \| Security	6	5
12 months or longer, Fair value	$ 13,902	$ 16,842
12 months or longer, Unrealized losses	$ (291)	$ (229)
Redeemable Preferred Stock [Member] \| Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	5	12
Less than 12 months, Fair value	$ 764	$ 1,153
Less than 12 months, Unrealized losses	$ (29)	$ (9)
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)
Common Stock [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	3	2
Less than 12 months, Fair value	$ 8,690	$ 87
Less than 12 months, Unrealized losses	$ (148)	$ (20)
12 months or longer, Number of issues \| Security	2	2
12 months or longer, Fair value	$ 93	$ 117
12 months or longer, Unrealized losses	$ (96)	$ (45)
Mutual Funds [Member] \| Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues \| Security	3	2
Less than 12 months, Fair value	$ 13,192	$ 10,514
Less than 12 months, Unrealized losses	$ (374)	$ (97)
12 months or longer, Number of issues \| Security	1	1
12 months or longer, Fair value	$ 7,867	$ 8,859
12 months or longer, Unrealized losses	$ (3,400)	$ (1,827)

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=27724398&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=27724398&loc=d3e27337-111563

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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=27724398&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=27724398&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=27724398&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=27724398&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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