Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes (Textual) [Abstract]
Taxes (benefits) relating to changes in unfunded status of the supplemental retirement plans	$ 429,000	$ 904,000	$ (2,984,000)
Taxes (benefits) related to unrealized gains and losses on available-for-sale investment securities	(4,631,000)	(797,000)	(68,000)
Taxes (benefits) related to employee stock options	(170,000)	(28,000)	(293,000)
Carrying value of low income housing tax credit funds	18,465,000	4,223,000	$ 0
Low income housing tax credit fund commitments	15,176,000	3,330,000
Unrecognized tax benefit	114,000	168,000
Interest	0	0
Penalties	0	$ 0
North Valley Bancorp [Member]
Income Taxes (Textual) [Abstract]
Unrecognized tax benefits, if recognized	114,000
Unrecognized tax benefit	73,000
Federal [Member]
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards	4,600,000
Capital loss carryforwards	111,000
Tax credit carryforwards	69,000
California [Member]
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards	26,000,000
Capital loss carryforwards	388,000
Tax credit carryforwards	$ 2,700,000