Income Taxes - Valuation Allowance Activity on Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Balance at Beginning of Year	$ 8,155	$ 111,950	$ 116,110
Additions	0	0	4,036
Reductions	(1,104)	(103,795)	(8,196)
Balance at End of Year	$ 7,051	$ 8,155	$ 111,950

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant