Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes (Textual) [Abstract]
Unfunded status of the supplemental retirement plans, net of tax	$ (3,324,000)	$ (4,570,000)	$ (1,269,000)
Unrealized gains and losses on available-for-sale investment securities	(797,000)	(68,000)	(1,780,000)
Taxes (benefits) related to employee stock options	479,000	97,000	$ 138,000
Tax credits and other tax benefits relating to investments	354,000
Amortization expense	277,000	0
Carrying value of low income housing tax credit funds	4,223,000
Low income housing tax credit fund commitments	3,330,000
Unrecognized tax benefit	168,000	227,000
Interest	0	0
Penalties	0	$ 0
North Valley Bancorp [Member]
Income Taxes (Textual) [Abstract]
Unrecognized tax benefits, if recognized	182,000
Unrecognized tax benefit	116,000
Federal [Member]
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards	9,200,000
Capital loss carryforwards	78,000
Tax credit carryforwards	69,000
California [Member]
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards	30,700,000
Capital loss carryforwards	356,000
Tax credit carryforwards	$ 2,700,000