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	Mar. 31, 2014	Dec. 31, 2013
Description of assets
Total assets	$ 1,815	$ 3,159
Impaired loans-non-covered [Member] \| Commercial and Industrial [Member]
Description of assets
Total assets	981	627
Impaired loans-non-covered [Member] \| Commercial Real Estate [Member]
Description of assets
Total assets	320
Impaired loans-non-covered [Member] \| Dairy & Livestock and Agribusiness [Member]
Description of assets
Total assets	420	2,096
Impaired loans-non-covered [Member] \| Consumer and Other Loans [Member]
Description of assets
Total assets	94	2
Covered Loans [Member]
Description of assets
Total assets		434
Level 1 [Member]
Description of assets
Total assets
Level 1 [Member] \| Impaired loans-non-covered [Member] \| Commercial and Industrial [Member]
Description of assets
Total assets
Level 1 [Member] \| Impaired loans-non-covered [Member] \| Commercial Real Estate [Member]
Description of assets
Total assets
Level 1 [Member] \| Impaired loans-non-covered [Member] \| Dairy & Livestock and Agribusiness [Member]
Description of assets
Total assets
Level 1 [Member] \| Impaired loans-non-covered [Member] \| Consumer and Other Loans [Member]
Description of assets
Total assets
Level 1 [Member] \| Covered Loans [Member]
Description of assets
Total assets
Level 2 [Member]
Description of assets
Total assets
Level 2 [Member] \| Impaired loans-non-covered [Member] \| Commercial and Industrial [Member]
Description of assets
Total assets
Level 2 [Member] \| Impaired loans-non-covered [Member] \| Commercial Real Estate [Member]
Description of assets
Total assets
Level 2 [Member] \| Impaired loans-non-covered [Member] \| Dairy & Livestock and Agribusiness [Member]
Description of assets
Total assets
Level 2 [Member] \| Impaired loans-non-covered [Member] \| Consumer and Other Loans [Member]
Description of assets
Total assets
Level 2 [Member] \| Covered Loans [Member]
Description of assets
Total assets
Level 3 [Member]
Description of assets
Total assets	7,133	12,934
Level 3 [Member] \| Impaired loans-non-covered [Member] \| Commercial and Industrial [Member]
Description of assets
Total assets	3,068	529
Level 3 [Member] \| Impaired loans-non-covered [Member] \| Commercial Real Estate [Member]
Description of assets
Total assets	1,871
Level 3 [Member] \| Impaired loans-non-covered [Member] \| Dairy & Livestock and Agribusiness [Member]
Description of assets
Total assets	2,100	11,899
Level 3 [Member] \| Impaired loans-non-covered [Member] \| Consumer and Other Loans [Member]
Description of assets
Total assets	94	2
Level 3 [Member] \| Covered Loans [Member]
Description of assets
Total assets		504
Carrying Value [Member]
Description of assets
Total assets	7,133	12,934
Carrying Value [Member] \| Impaired loans-non-covered [Member] \| Commercial and Industrial [Member]
Description of assets
Total assets	3,068	529
Carrying Value [Member] \| Impaired loans-non-covered [Member] \| Commercial Real Estate [Member]
Description of assets
Total assets	1,871
Carrying Value [Member] \| Impaired loans-non-covered [Member] \| Dairy & Livestock and Agribusiness [Member]
Description of assets
Total assets	2,100	11,899
Carrying Value [Member] \| Impaired loans-non-covered [Member] \| Consumer and Other Loans [Member]
Description of assets
Total assets	94	2
Carrying Value [Member] \| Covered Loans [Member]
Description of assets
Total assets		$ 504