Portion of Net Unrealized Gains (Losses) Recognized to Equity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Gain (Loss) on Investments [Line Items]
Net Unrealized Gains (Losses) recognized	$ 26,769	$ (3,181)
Equity Securities
Gain (Loss) on Investments [Line Items]
Total Net Realized and Unrealized Gains (Losses) recognized	26,526	(3,396)
Less: Net Realized Losses on Investments Sold	(243)	(215)
Net Unrealized Gains (Losses) recognized	$ 26,769	$ (3,181)

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

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 gain (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 unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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