Fair Value Information - Assets and Liabilities Measured at Fair Value on Non-Recurring Basis (Detail) (Fair Value on Non-Recurring Basis [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Description of assets
Total assets	$ 2,846	$ 3,159
Other real estate owned [Member]
Description of assets
Total assets	0	434
Loans, Excluding PCI Loans [Member] | Commercial and industrial [Member]
Description of assets
Total assets	771	627
Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Description of assets
Total assets	296
Loans, Excluding PCI Loans [Member] | Commercial real estate [Member]
Description of assets
Total assets	271	0
Loans, Excluding PCI Loans [Member] | Construction [Member]
Description of assets
Total assets	0	0
Loans, Excluding PCI Loans [Member] | SFR mortgage [Member]
Description of assets
Total assets	0	0
Loans, Excluding PCI Loans [Member] | Dairy & livestock and agribusiness [Member]
Description of assets
Total assets	1,061	2,096
Loans, Excluding PCI Loans [Member] | Consumer and other loans [Member]
Description of assets
Total assets	447	2
Level 1 [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Other real estate owned [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | Commercial and industrial [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Description of assets
Total assets	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | Commercial real estate [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | Construction [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | SFR mortgage [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | Dairy & livestock and agribusiness [Member]
Description of assets
Total assets	0	0
Level 1 [Member] | Loans, Excluding PCI Loans [Member] | Consumer and other loans [Member]
Description of assets
Total assets	0	0
Level 2 [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Other real estate owned [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | Commercial and industrial [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Description of assets
Total assets	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | Commercial real estate [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | Construction [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | SFR mortgage [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | Dairy & livestock and agribusiness [Member]
Description of assets
Total assets	0	0
Level 2 [Member] | Loans, Excluding PCI Loans [Member] | Consumer and other loans [Member]
Description of assets
Total assets	0	0
Level 3 [Member]
Description of assets
Total assets	6,323	12,934
Level 3 [Member] | Other real estate owned [Member]
Description of assets
Total assets	0	504
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | Commercial and industrial [Member]
Description of assets
Total assets	1,911	529
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Description of assets
Total assets	1,327
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | Commercial real estate [Member]
Description of assets
Total assets	2,500	0
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | Construction [Member]
Description of assets
Total assets	0	0
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | SFR mortgage [Member]
Description of assets
Total assets	0	0
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | Dairy & livestock and agribusiness [Member]
Description of assets
Total assets	103	11,899
Level 3 [Member] | Loans, Excluding PCI Loans [Member] | Consumer and other loans [Member]
Description of assets
Total assets	482	2
Carrying Value [Member]
Description of assets
Total assets	6,323	12,934
Carrying Value [Member] | Other real estate owned [Member]
Description of assets
Total assets	0	504
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | Commercial and industrial [Member]
Description of assets
Total assets	1,911	529
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | Small Business Administration [Member]
Description of assets
Total assets	1,327
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | Commercial real estate [Member]
Description of assets
Total assets	2,500	0
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | Construction [Member]
Description of assets
Total assets	0	0
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | SFR mortgage [Member]
Description of assets
Total assets	0	0
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | Dairy & livestock and agribusiness [Member]
Description of assets
Total assets	103	11,899
Carrying Value [Member] | Loans, Excluding PCI Loans [Member] | Consumer and other loans [Member]
Description of assets
Total assets	$ 482	$ 2