Noninterest Income and Expense - Components of Noninterest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule Of Other Noninterest Income And Expense [Line Items]
Base salaries, net of deferred loan origination costs	$ 13,419				$ 11,562			$ 39,095	$ 34,808
Incentive compensation	2,798				1,674			7,008	4,660
Benefits and other compensation costs	4,643				4,297			14,067	13,407
Total salaries and benefits expense	20,860				17,533			60,170	52,875
Occupancy	2,667				2,599			7,504	7,557
Equipment	1,607				1,417			4,837	4,358
Data processing and software	2,068				1,869			6,266	5,655
ATM network charges	1,133				757			3,141	2,512
Telecommunications	702				658			2,085	2,329
Postage	381				314			1,186	956
Courier service	280				303			816	804
Advertising	1,049				926			3,021	2,736
Assessments	654				642			1,864	1,987
Operational losses	497				201			1,006	474
Professional fees	1,018				999			3,183	3,153
Foreclosed assets expense	37				105			197	305
Provision for foreclosed asset losses	9				106			40	347
Reserve for unfunded commitments	25				(40)			433	(60)
Intangible amortization	359				289			1,017	867
Merger expense								784	586
Litigation contingent liability								1,450
Other	4,070				2,761			10,434	8,716
Total other noninterest expense	16,556				13,906			49,264	43,282
Total noninterest expense	$ 37,416	$ 38,267	$ 33,751	$ 34,684	$ 31,439	$ 32,436	$ 32,282	109,434	96,157
North Valley Bancorp [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Base salaries (outside temporary help)								187
Equipment								35
Data processing and software									108
Professional fees								342	120
Advertising and marketing								114
Merger expense								784	586
Other								$ 106	$ 358