Investment Securities - Additional Information (Detail) (USD $)	6 Months Ended
Jun. 30, 2013 Investment	Jun. 30, 2012	Dec. 31, 2012 Investment
Investments Debt And Equity Securities [Abstract]
Carrying value of securities pledged to secure public deposits and for other purposes as required by law	$ 305,700,000		$ 368,200,000
Realized other-than-temporary impairment charges to noninterest income on equity portfolio	$ 0	$ 9,000
Number of investments in non federal issuer representing more than 10% of shareholders' equity	0		0
Maximum investment in any single non-federal issuer representing shareholders' equity	10.00%		10.00%

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8B

-URI http://asc.fasb.org/extlink&oid=27724398&loc=SL6284393-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration