Noninterest Income and Expense - Components of Noninterest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule Of Other Noninterest Income And Expense [Line Items]
Base salaries, net of deferred loan origination costs	$ 11,562				$ 9,066			$ 34,808	$ 26,940
Incentive compensation	1,674				1,265			4,660	3,593
Benefits and other compensation costs	4,297				3,038			13,407	9,456
Total salaries and benefits expense	17,533				13,369			52,875	39,989
Occupancy	2,599				1,971			7,557	5,735
Equipment	1,417				995			4,358	3,091
Data processing and software	1,869				1,577			5,655	4,105
ATM network charges	757				657			2,512	2,010
Telecommunications	658				648			2,329	1,941
Postage	314				179			956	627
Courier service	303				269			804	727
Advertising	926				581			2,736	1,264
Assessments	642				493			1,987	1,495
Operational losses	201				138			474	465
Professional fees	999				903			3,153	2,792
Foreclosed assets expense	105				94			305	403
Provision for foreclosed asset losses	106				98			347	137
Reserve for unfunded commitments	(40)				175			(60)	(195)
Intangible amortization	289				53			867	157
Merger expense					625			586	1,268
Other	2,761				2,555			8,716	7,802
Total other noninterest expense	13,906				12,011			43,282	33,824
Total noninterest expense	$ 31,439	$ 32,436	$ 32,282	$ 36,566	25,380	$ 25,116	$ 23,317	96,157	73,813
North Valley Bancorp [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Data processing and software					60			108	60
Professional fees					565			120	1,033
Merger expense					$ 625			586	1,268
Other								$ 358	$ 175