Junior Subordinated Debt - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($) Location Trust	Dec. 31, 2017 USD ($)	Oct. 03, 2014 USD ($)
Class of Stock [Line Items]
Number of subsidiary business trusts | Trust	5
Trust preferred securities amount	$ 62,889,000
Subordinated debenture, recorded fair value	$ 56,950,000	$ 56,858,000
Number of locations organized | Location	2
Change in junior subordinated debt	$ 92,000
Capital Trusts [Member]
Class of Stock [Line Items]
Trust preferred securities amount	62,900,000
North Valley Trust II [Member]
Class of Stock [Line Items]
Trust preferred securities amount	6,186,000
Subordinated debenture, recorded fair value	5,154,000	5,135,000	$ 5,006,000
North Valley Trust III [Member]
Class of Stock [Line Items]
Trust preferred securities amount	5,155,000
Subordinated debenture, recorded fair value	4,060,000	4,041,000	3,918,000
North Valley Trust IV [Member]
Class of Stock [Line Items]
Trust preferred securities amount	10,310,000
Subordinated debenture, recorded fair value	$ 6,498,000	$ 6,444,000	$ 6,063,000
North Valley Bancorp [Member]
Class of Stock [Line Items]
Number of locations acquired | Location	3
Acquisition, completion date	Oct. 03, 2014
Maximum [Member]
Class of Stock [Line Items]
Consecutive payments of interest on debenture defer Period	5 years