Mortgage Servicing Rights - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2013	Dec. 31, 2012
Mortgage Servicing Rights [Line Items]
Aggregate fair value of mortgage servicing rights	$ 7.0	$ 4.2
Minimum [Member]
Mortgage Servicing Rights [Line Items]
Range of fair value of mortgage servicing rights using discount rates	5.10%	5.00%
Maximum [Member]
Mortgage Servicing Rights [Line Items]
Range of fair value of mortgage servicing rights using discount rates	10.00%	10.00%

Fair value of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122739-111746

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=7516967&loc=d3e66267-113978

Name:	us-gaap_ServicingAssetAtAmortizedValueFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant