Fair Value - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Carrying value of loans fully charged off	0
Other real estate owned [Member] | Impaired loans [Member] | Minimum [Member]
Term period for external appraisals	6 months
Other real estate owned [Member] | Impaired loans [Member] | Maximum [Member]
Term period for external appraisals	12 months