Borrowings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Federal funds purchased and securities sold under agreements to repurchase
Maximum amount outstanding at any month end	$ 149,316	$ 154,440	$ 125,920
Weighted average interest rate at end of year	0.21%	0.22%	0.25%
Average amount outstanding	$ 141,592	$ 106,495	$ 87,106
Weighted average interest rate during the year	0.24%	0.26%	0.27%

Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of short-term debt outstanding by type or by instrument at that time.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph b

-Article 5

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant