Commitments and Contingencies - Summary of Financial Instruments Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Commitments And Contingencies Disclosure [Abstract]
Commitments to grant loans, Contract Amount	$ 329,833	$ 192,295
Unfunded commitments under lines of credit, Contract Amount	2,533,921	2,372,971
Commercial and standby letters of credit, Contract Amount	$ 77,201	$ 62,207

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant