Loans and Lease Finance Receivables and Allowance for Loan Losses - Summary of Loan, Excluding PCI Loans by Internal Risk Ratings (Detail) (Loans, Excluding PCI Loans [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 390,011	$ 376,800
SBA	134,265	135,992
Commercial real estate, Owner occupied	790,367	729,951
Commercial real estate, Non-owner occupied	1,697,436	1,477,564
Construction, Speculative	36,574	27,778
Construction, Non-speculative	18,599
Construction, Non-speculative		19,331
SFR mortgage	205,124	189,233
Dairy & livestock and agribusiness	279,173	294,292
Municipal lease finance receivables	77,834	89,106
Consumer and other loans	69,884	55,103
Total gross loans, excluding PCI loans	3,699,267	3,395,150
Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	234,029	228,976
SBA	84,769	83,951
Commercial real estate, Owner occupied	552,072	449,853
Commercial real estate, Non-owner occupied	1,347,006	1,104,065
Construction, Speculative	28,310	8,611
Construction, Non-speculative	18,071
Construction, Non-speculative		6,940
SFR mortgage	174,311	152,500
Dairy & livestock and agribusiness	174,783	43,588
Municipal lease finance receivables	35,463	43,445
Consumer and other loans	62,904	43,225
Total gross loans, excluding PCI loans	2,711,718	2,165,154
Watch List [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	105,904	100,016
SBA	24,124	28,052
Commercial real estate, Owner occupied	159,908	147,165
Commercial real estate, Non-owner occupied	241,809	242,431
Construction, Speculative	613	21
Construction, Non-speculative	528
Construction, Non-speculative		3,190
SFR mortgage	20,218	20,485
Dairy & livestock and agribusiness	85,660	86,580
Municipal lease finance receivables	22,349	18,338
Consumer and other loans	2,233	6,938
Total gross loans, excluding PCI loans	663,346	653,216
Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	33,795	38,219
SBA	15,858	15,198
Commercial real estate, Owner occupied	46,248	74,999
Commercial real estate, Non-owner occupied	56,353	81,088
Construction, Speculative	0	1,529
Construction, Non-speculative	0
Construction, Non-speculative		0
SFR mortgage	2,442	3,302
Dairy & livestock and agribusiness	8,612	92,514
Municipal lease finance receivables	20,022	20,893
Consumer and other loans	1,789	3,449
Total gross loans, excluding PCI loans	185,119	331,191
Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	16,031	9,560
SBA	7,920	8,390
Commercial real estate, Owner occupied	32,139	57,934
Commercial real estate, Non-owner occupied	52,268	49,980
Construction, Speculative	7,651	17,617
Construction, Non-speculative	0
Construction, Non-speculative		9,201
SFR mortgage	8,153	12,946
Dairy & livestock and agribusiness	10,015	69,005
Municipal lease finance receivables	0	6,430
Consumer and other loans	2,763	1,491
Total gross loans, excluding PCI loans	136,940	242,554
Doubtful & Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	252	29
SBA	1,594	401
Commercial real estate, Owner occupied	0	0
Commercial real estate, Non-owner occupied	0	0
Construction, Speculative	0	0
Construction, Non-speculative	0
Construction, Non-speculative		0
SFR mortgage	0	0
Dairy & livestock and agribusiness	103	2,605
Municipal lease finance receivables	0	0
Consumer and other loans	195	0
Total gross loans, excluding PCI loans	$ 2,144	$ 3,035