Realized Gains and Losses on Investment Sold, Excluding Net Other-Than-Temporary Impairment Losses Recognized in Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Gain (Loss) on Investments [Line Items]
Net Realized Gains (Losses) on Investments Sold	$ 393	$ 1,169
Fixed Maturities
Gain (Loss) on Investments [Line Items]
Gains	784	1,806
Losses	(265)	(275)
Net Realized Gains (Losses) on Investments Sold	519	1,531
Short-Term Investments, Cash & Cash Equivalents
Gain (Loss) on Investments [Line Items]
Gains		18
Losses	(17)	(174)
Net Realized Gains (Losses) on Investments Sold	(17)	(156)
Other Invested Assets
Gain (Loss) on Investments [Line Items]
Gains	134	50
Losses		(41)
Net Realized Gains (Losses) on Investments Sold	134	9
Equity Securities
Gain (Loss) on Investments [Line Items]
Gains	3
Losses	(246)	(215)
Net Realized Gains (Losses) on Investments Sold	$ (243)	$ (215)

Amount of gross realized gain from sale of marketable securities.

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Amount of gross realized loss from sale of marketable securities. Excludes other than temporary impairments (OTTI).

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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), excluding other-than-temporary impairment (OTTI).

+ References

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), excluding other-than-temporary impairment (OTTI).

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Amount of realized gain from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

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Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117546-209714

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Amount of realized loss from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of realized gain (loss) on investment in marketable security, excluding other-than-temporary impairment (OTTI).

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