Goodwill and Other Intangible Assets - Additional Information (Detail)	Mar. 18, 2016 USD ($) Branches	Oct. 03, 2014 USD ($)	Sep. 23, 2011 USD ($)	May 28, 2010 USD ($)
North Valley Bancorp [Member]
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles		$ 6,614,000
Citizens [Member]
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles			$ 898,000
Bank of America [Member]
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles	$ 2,046,000
Number of branches | Branches	3
Granite [Member]
Finite-Lived Intangible Assets [Line Items]
Additions to core deposit intangibles				$ 562,000