Fair Value Information - Assets and Liabilities Measured at Fair Value on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Description of assets
Impaired loans-non-covered	$ (2,164)	$ (3,930)
OREO-non-covered	(73)	(336)
OREO-covered		(467)
Total assets	(2,237)	(4,733)
Level 1 [Member]
Description of assets
Impaired loans-non-covered
OREO-non-covered
OREO-covered
Total assets
Level 2 [Member]
Description of assets
Impaired loans-non-covered
OREO-non-covered
OREO-covered
Total assets
Level 3 [Member]
Description of assets
Impaired loans-non-covered	4,169	12,460
OREO-non-covered	828	3,008
OREO-covered		1,067
Total assets	4,997	16,535
Carrying Value [Member]
Description of assets
Impaired loans-non-covered	4,169	12,460
OREO-non-covered	828	3,008
OREO-covered		1,067
Total assets	$ 4,997	$ 16,535