Transfers and Servicing of Financial Assets (Including Mortgage Banking Activity) - Schedule of Mortgage Servicing Rights at Carrying Values (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Acquired Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 46,754	$ 46,754
Accumulated Amortization	(27,877)	(26,694)
Net Carrying Amount	18,877	20,060
Mortgage servicing rights [Member]
Acquired Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	1,426	1,234
Accumulated Amortization	(375)	(304)
Net Carrying Amount	$ 1,051	$ 930

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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