Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended
	Jan. 01, 2020 USD ($)	Dec. 31, 2021 USD ($) trust segment office county	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Significant Of Accounting Policies [Line Items]
Number of subsidiary business trusts (in trusts) | trust		5
Number of loan production offices (in offices) | office		2
Company's investments in the trusts		$ 1,744,000
Number of business segments (in segments) | segment		1
Net unrealized gains (losses)		$ 718,000	$ (64,000)
Total shareholders' equity		1,000,184,000	925,114,000	$ 906,570,000	$ 827,373,000
Gain (loss) on marketable equity securities		(86,000)	64,000	86,000
Accrued interest write off		0	0	0
Security credit losses recognized		0	0	0
Credit loss		0	0	0
ASU 2016-13
Significant Of Accounting Policies [Line Items]
Allowance for credit loss	$ 18,913,000
Financing receivable, purchased with credit deterioration, discount (premium)	(481,000)
Retained Earnings
Significant Of Accounting Policies [Line Items]
Total shareholders' equity		$ 466,959,000	$ 381,999,000	367,794,000	$ 303,490,000
Retained Earnings | ASU 2016-13
Significant Of Accounting Policies [Line Items]
Taxes	5,449,000
Cumulative effect from change in accounting policies	$ 12,983,000
Cumulative Effect, Period of Adoption, Adjustment
Significant Of Accounting Policies [Line Items]
Total shareholders' equity				(12,983,000)
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Significant Of Accounting Policies [Line Items]
Total shareholders' equity				$ (12,983,000)
California
Significant Of Accounting Policies [Line Items]
Number of counties (in counties) | county		31
Minimum
Significant Of Accounting Policies [Line Items]
Loans held-for-sale, term		5 years
Regulatory liability, amortization period		15 years
Maximum
Significant Of Accounting Policies [Line Items]
Loans held-for-sale, term		10 years
Regulatory liability, amortization period		30 years
North Valley Bancorp
Significant Of Accounting Policies [Line Items]
Number of subsidiary business trusts (in trusts) | trust		3
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