Noninterest Income and Expense - Components of Noninterest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Other Noninterest Income And Expense [Line Items]
Base salaries, net of deferred loan origination costs									$ 53,169	$ 46,822	$ 39,342
Incentive compensation									8,872	6,964	5,068
Benefits and other compensation costs									18,683	17,619	13,134
Total salaries and benefits expense									80,724	71,405	57,544
Occupancy									10,139	10,126	8,203
Equipment									6,597	5,997	4,514
Data processing and software									8,846	7,670	6,512
Assessments									2,105	2,572	2,107
ATM & POS network charges									4,999	4,190	2,996
Advertising									3,829	3,992	2,413
Professional fees									5,409	4,545	3,888
Telecommunications									2,749	3,007	2,870
Postage									1,603	1,296	949
Courier service									998	1,154	1,055
Foreclosed assets expense									266	490	528
Intangible amortization									1,377	1,157	446
Operational losses									1,564	737	764
Provision for foreclosed asset losses									140	502	208
Reserve for unfunded commitments									244	330	(395)
Legal settlement									1,450
Merger & acquisition expense									784	586	4,858
Miscellaneous other									12,174	11,085	10,919
Total other noninterest expense									65,273	59,436	52,835
Total noninterest expense	$ 36,563	$ 37,416	$ 38,267	$ 33,751	$ 34,684	$ 31,439	$ 32,436	$ 32,282	145,997	130,841	110,379
North Valley Bancorp [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Base salaries, net of loan origination costs									187
Data processing and software										108	475
Professional fees									342	120	2,390
Merger & acquisition expense									784	586	4,858
Miscellaneous other									$ 255	$ 358	725
North Valley Bancorp [Member] | Incentive Compensation [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Merger & acquisition expense											1,174
North Valley Bancorp [Member] | Benefits and Other Compensation Costs [Member]
Schedule Of Other Noninterest Income And Expense [Line Items]
Merger & acquisition expense											$ 94