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.

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Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Divestitures - Additional Information (Detail) - USD ($)	3 Months Ended					12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on divestitures and sale of investments	$ 403,000	$ (9,000)	$ (14,000)	$ (1,619,000)	$ 20,054,000	$ 394,000	$ 18,421,000
Other Sales [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (loss) on divestitures and sale of investments						$ 0	$ 18,400,000	$ 0