Fair Value of Financial Instruments - Additional Information (Detail)	12 Months Ended
Dec. 31, 2011 Minimum [Member]	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2012 Core Deposits [Member] Minimum [Member]	Dec. 31, 2012 Core Deposits [Member] Maximum [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Amortized estimated useful life	3 years	10 years	3 years	10 years

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration