Investments - Summary of Details on Realized and Unrealized Gains and Losses Related to Equity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Unrealized gains (losses) recognized during the reported period on equity securities still held at the end of the reported period	$ (519)	$ (8,024)

Amount of unrealized gain (loss) on investment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Name:	us-gaap_UnrealizedGainLossOnInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration