Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Fair Value Disclosures [Abstract]
Transfers between Level 1 and Level 2	$ 0	$ 0
Weighted Average Collateral Severity Rate	36.00%	37.00%
Minimum period to update carrying values for real estate owned properties	45 days

Amount of transfers of financial instruments classified in shareholders' equity measured on a recurring basis out of level 1 of the fair value hierarchy into level 2.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Name:	us-gaap_FairValueEquityLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant