Goodwill and Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Goodwill And Core Deposit Intangibles [Line Items]
Core deposit intangible assets		$ 1,149,000		$ 1,672,000
Goodwill	956,000
Aggregate amortization expense for intangible assets		$ 1,359,000	$ 1,011,000	$ 999,000
Minimum [Member]
Goodwill And Core Deposit Intangibles [Line Items]
Amortization period of core deposit Intangibles	3
Maximum [Member]
Goodwill And Core Deposit Intangibles [Line Items]
Amortization period of core deposit Intangibles	10