Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Goodwill and Other Intangible Assets - Additional Information (Detail) $ in Thousands		12 Months Ended
	Mar. 18, 2016 USD ($) Branches	Dec. 31, 2019 USD ($)	Jul. 06, 2018 USD ($)	Oct. 03, 2014 USD ($)	Sep. 23, 2011 USD ($)
Finite-Lived Intangible Assets [Line Items]
Impairment charges		$ 0
FNBB
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles			$ 27,605
North Valley Bancorp
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles				$ 6,614
Citizens
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles					$ 898
Bank of America
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles	$ 2,046
Number of branches (in branches) \| Branches	3