Noninterest Income and Expense - Components of Noninterest Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Schedule Of Other Noninterest Income And Expense [Line Items]
Base salaries, net of deferred loan origination costs	$ 11,744				$ 8,866
Incentive compensation	1,596				1,123
Benefits and other compensation costs	4,760				3,314
Total salaries and benefits expense	18,100				13,303
Occupancy	2,417				1,962
Equipment	1,414				1,036
Data processing and software	1,952				1,178
ATM network charges	770				643
Telecommunications	886				580
Postage	312				227
Courier service	248				234
Advertising	808				342
Assessments	651				521
Operational losses	124				177
Professional fees	1,119				614
Foreclosed assets expense	98				158
Provision for foreclosed asset losses	67				36
Reserve for unfunded commitments	(130)				(185)
Intangible amortization	289				52
Merger expense	586				225
Other	2,571				2,214
Total other noninterest expense	14,182				10,014
Total noninterest expense	32,282	36,566	25,380	25,116	23,317
Merger expense:
Merger expense	586				225
Merger expense	586				225
North Valley Bancorp [Member] | Data processing and software [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Merger expense	108
Merger expense:
Merger expense	108
Merger expense	108
North Valley Bancorp [Member] | Professional fees [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Merger expense	120				225
Merger expense:
Merger expense	120				225
Merger expense	120				225
North Valley Bancorp [Member] | Other [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Merger expense	358
Merger expense:
Merger expense	358
Merger expense	$ 358