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Number Of Loan Production Offices

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Summary of Significant Accounting Policies - Additional Information (Detail)	2 Months Ended	12 Months Ended
	Mar. 02, 2020 USD ($)	Dec. 31, 2019 USD ($) Trust Segment Office Business	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2016 USD ($)
Significant Of Accounting Policies [Line Items]
Number of subsidiary business trusts \| Trust		5
Number of loan production offices \| Office		2
Company's investments in the trusts		$ 1,719,000
Number of business segment \| Segment		1
Marketable securities recorded		$ 2,960,000	$ 2,874,000	$ 2,874,000
Unrealized gains (losses) recognized in condensed consolidated statements of income		86,000	(64,000)
Recognized OTTI losses		$ 0	0	0
TDR loans payment period in nonaccrual status		6 months
Allowance of loan losses		$ 30,616,000	$ 32,582,000	$ 30,323,000		$ 32,503,000
North Valley Bancorp
Significant Of Accounting Policies [Line Items]
Number of subsidiary business trusts \| Trust		3
California
Significant Of Accounting Policies [Line Items]
Number of counties \| Business		29
Adoption ASU 2016-01 \| Deferred Tax Assets
Significant Of Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle cumulative effect of change on equity or net assets					$ (18,000)
Adoption ASU 2016-01 \| Retained Earnings
Significant Of Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle cumulative effect of change on equity or net assets					$ (62,000)
Minimum \| ASU 2016-13 \| Scenario, Forecast
Significant Of Accounting Policies [Line Items]
Allowance of loan losses	$ 42,000,000
Increase in allowance for loan and losses	11,384,000
Decline in equity, net of tax	(8,020,000)
Maximum \| ASU 2016-13 \| Scenario, Forecast
Significant Of Accounting Policies [Line Items]
Allowance of loan losses	50,000,000
Increase in allowance for loan and losses	19,384,000
Decline in equity, net of tax	$ (13,655,000)
Furniture and Equipment \| Minimum
Significant Of Accounting Policies [Line Items]
Estimated useful lives of the related assets or lease terms		3 years
Furniture and Equipment \| Maximum
Significant Of Accounting Policies [Line Items]
Estimated useful lives of the related assets or lease terms		10 years
Land Improvements and Buildings \| Minimum
Significant Of Accounting Policies [Line Items]
Estimated useful lives of the related assets or lease terms		15 years
Land Improvements and Buildings \| Maximum
Significant Of Accounting Policies [Line Items]
Estimated useful lives of the related assets or lease terms		40 years