Introduction and Basis of Presentation - Additional Information (Detail)	Dec. 31, 2012 State Location
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Minimum number of domestic branch offices	300
States with domestic branch offices	45

The number of states the entity operates in as of the balance sheet date.

No definition available.

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant