Investments - Summary of Unrealized Gains and Losses in Consolidated Statement of Income (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) recognized	$ 2,884	$ 1,326	$ (1,921)	$ 6,619
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Net gains (losses) recognized	2,892	1,193	(3,884)	6,030
Exclude: Net realized gains (losses) recognized for securities sold	8	(133)	(1,963)	(589)
Net unrealized gains (losses) recognized	$ 2,884	$ 1,326	$ (1,921)	$ 6,619

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=116654751&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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