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Investments - Realized and Unrealized Gains and Losses for Marketable Equity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Net realized investment gain	$ (97)	$ 470
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Net realized investment gain	(1)
Unrealized gains (losses) on equity securities held	(23)
Total gain (loss) recognized, net	$ (24)

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- Definition

Available-for-sale securities, gross realized and unrealized gain (loss), net.

+ References

No definition available.

+ Details

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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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- Definition

Amount of unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities.

+ References

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

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- Definition

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.

+ References

No definition available.

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