Income Taxes (Textual) [Abstract]

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Investment in low income housing tax credit funds.

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Low income housing tax credit fund commitments.

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Tax cuts and jobs act of 2017 acceleration of amortization expense on low income housing tax credit investments deferred tax expense benefit.

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Tax cuts and jobs act of 2017 remeasurement of deferred taxes deferred tax expense benefit.

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- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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The amount of estimated interest recognized in the period arising from income tax examinations.

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The amount of estimated penalties recognized in the period arising from income tax examinations.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Amount, before reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Amount of unrecognized tax benefits.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes (Textual) [Abstract]
Federal corporate tax rate		35.00%	35.00%	35.00%
Deferred tax expense		$ 7,416,000
Amortization expense on the low income housing tax credit		226,000
Taxes relating to changes in unfunded status of the supplemental retirement plans		(400,000)	$ (429,000)	$ (904,000)
Taxes (benefits) related to unrealized gains and losses on available-for-sale investment securities		2,722,000	(4,631,000)	(797,000)
Taxes (benefits) related to employee stock options		0	(170,000)	$ (28,000)
Carrying value of low income housing tax credit funds		16,854,000	18,465,000
Low income housing tax credit fund commitments		8,554,000	15,176,000
Unrecognized tax benefit		60,000	114,000
Interest		0	0
Penalties		0	$ 0
Scenario, Forecast [Member]
Income Taxes (Textual) [Abstract]
Federal corporate tax rate	21.00%
North Valley Bancorp [Member]
Income Taxes (Textual) [Abstract]
Unrecognized tax benefits, if recognized		60,000
Unrecognized tax benefit		34,000
Federal [Member]
Income Taxes (Textual) [Abstract]
Tax credit carryforwards		69,000
California [Member]
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards		21,400,000
Tax credit carryforwards		$ 648,000