Allowance for Credit Losses - Impaired Loans (Details) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	$ 9,529,000		$ 9,529,000		$ 2,875,000
Upaid Principal Balance, With no related allowance recorded	11,752,000		11,752,000		3,722,000
Recorded Investment, With an allowance recorded	4,488,000		4,488,000		14,230,000
Unpaid Principal Balance, With an allowance recorded	5,140,000		5,140,000		15,336,000
Related Allowance	1,081,000		1,081,000		510,000
Total Recorded Investment	14,017,000		14,017,000		17,105,000
Total Unpaid Principal Balance	16,892,000		16,892,000		19,058,000
Average Recorded Investment, With no related allowance recorded	7,183,000	7,985,000	7,249,000	9,299,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	7,362,000	9,640,000	7,763,000	9,457,000
Interest Income Recognized, With an allowance recorded	135,000	142,000	400,000	463,000
Average Recorded Investment, Total	14,545,000	17,625,000	15,012,000	18,756,000
Interest Income Recognized, Total	135,000	142,000	400,000	463,000
Forgone interest on nonaccrual loans	145,000	181,000	523,000	525,000
Commercial
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	393,000		393,000		0
Upaid Principal Balance, With no related allowance recorded	423,000		423,000		0
Recorded Investment, With an allowance recorded	1,256,000		1,256,000		2,405,000
Unpaid Principal Balance, With an allowance recorded	1,284,000		1,284,000		2,405,000
Related Allowance	632,000		632,000		40,000
Average Recorded Investment, With no related allowance recorded	412,000	600,000	309,000	1,235,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	1,271,000	1,849,000	1,404,000	1,624,000
Interest Income Recognized, With an allowance recorded	15,000	50,000	80,000	178,000
Commercial and industrial
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	393,000		393,000		0
Upaid Principal Balance, With no related allowance recorded	423,000		423,000		0
Recorded Investment, With an allowance recorded	1,256,000		1,256,000		2,405,000
Unpaid Principal Balance, With an allowance recorded	1,284,000		1,284,000		2,405,000
Related Allowance	632,000		632,000		40,000
Average Recorded Investment, With no related allowance recorded	412,000	600,000	309,000	1,235,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	1,271,000	1,849,000	1,404,000	1,624,000
Interest Income Recognized, With an allowance recorded	15,000	50,000	80,000	178,000
Agricultural land and production
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	0		0		0
Upaid Principal Balance, With no related allowance recorded	0		0		0
Recorded Investment, With an allowance recorded	0		0		0
Unpaid Principal Balance, With an allowance recorded	0		0		0
Related Allowance	0		0		0
Average Recorded Investment, With no related allowance recorded	0	0	0	0
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	0	0	0	0
Interest Income Recognized, With an allowance recorded	0	0	0	0
Real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	7,198,000		7,198,000		1,352,000
Upaid Principal Balance, With no related allowance recorded	8,623,000		8,623,000		1,888,000
Recorded Investment, With an allowance recorded	2,660,000		2,660,000		11,516,000
Unpaid Principal Balance, With an allowance recorded	3,278,000		3,278,000		12,608,000
Related Allowance	214,000		214,000		465,000
Average Recorded Investment, With no related allowance recorded	4,700,000	5,770,000	4,964,000	6,498,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	5,520,000	7,479,000	5,894,000	7,242,000
Interest Income Recognized, With an allowance recorded	120,000	92,000	320,000	285,000
Owner occupied
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	1,804,000		1,804,000		0
Upaid Principal Balance, With no related allowance recorded	2,643,000		2,643,000		0
Recorded Investment, With an allowance recorded	1,790,000		1,790,000		1,575,000
Unpaid Principal Balance, With an allowance recorded	1,963,000		1,963,000		1,733,000
Related Allowance	49,000		49,000		165,000
Average Recorded Investment, With no related allowance recorded	2,196,000	992,000	1,681,000	747,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	1,471,000	646,000	1,454,000	662,000
Interest Income Recognized, With an allowance recorded	35,000	0	65,000	0
Real estate construction and other land loans
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	5,227,000		5,227,000		1,352,000
Upaid Principal Balance, With no related allowance recorded	5,431,000		5,431,000		1,888,000
Recorded Investment, With an allowance recorded	870,000		870,000		9,941,000
Unpaid Principal Balance, With an allowance recorded	1,315,000		1,315,000		10,875,000
Related Allowance	165,000		165,000		300,000
Average Recorded Investment, With no related allowance recorded	2,172,000	4,778,000	3,001,000	5,551,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	4,049,000	6,833,000	4,440,000	6,387,000
Interest Income Recognized, With an allowance recorded	85,000	92,000	255,000	285,000
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	167,000		167,000		0
Upaid Principal Balance, With no related allowance recorded	549,000		549,000		0
Recorded Investment, With an allowance recorded	0		0		0
Unpaid Principal Balance, With an allowance recorded	0		0		0
Related Allowance	0		0		0
Average Recorded Investment, With no related allowance recorded	332,000	0	282,000	200,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	0	0	0	193,000
Interest Income Recognized, With an allowance recorded	0	0	0	0
Agricultural real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	0		0		0
Upaid Principal Balance, With no related allowance recorded	0		0		0
Recorded Investment, With an allowance recorded	0		0		0
Unpaid Principal Balance, With an allowance recorded	0		0		0
Related Allowance	0		0		0
Average Recorded Investment, With no related allowance recorded	0	0	0	0
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	0	0	0	0
Interest Income Recognized, With an allowance recorded	0	0	0	0
Other real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	0		0		0
Upaid Principal Balance, With no related allowance recorded	0		0		0
Recorded Investment, With an allowance recorded	0		0		0
Unpaid Principal Balance, With an allowance recorded	0		0		0
Related Allowance	0		0		0
Average Recorded Investment, With no related allowance recorded	0	0	0	0
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	0	0	0	0
Interest Income Recognized, With an allowance recorded	0	0	0	0
Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	1,938,000		1,938,000		1,523,000
Upaid Principal Balance, With no related allowance recorded	2,706,000		2,706,000		1,834,000
Recorded Investment, With an allowance recorded	572,000		572,000		309,000
Unpaid Principal Balance, With an allowance recorded	578,000		578,000		323,000
Related Allowance	235,000		235,000		5,000
Average Recorded Investment, With no related allowance recorded	2,071,000	1,615,000	1,976,000	1,566,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	571,000	312,000	465,000	591,000
Interest Income Recognized, With an allowance recorded	0	0	0	0
Equity loans and lines of credit
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	1,926,000		1,926,000		1,523,000
Upaid Principal Balance, With no related allowance recorded	2,691,000		2,691,000		1,834,000
Recorded Investment, With an allowance recorded	572,000		572,000		309,000
Unpaid Principal Balance, With an allowance recorded	578,000		578,000		323,000
Related Allowance	235,000		235,000		5,000
Average Recorded Investment, With no related allowance recorded	2,057,000	1,615,000	1,966,000	1,566,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	571,000	289,000	465,000	543,000
Interest Income Recognized, With an allowance recorded	0	0	0	0
Consumer and installment
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	12,000		12,000		0
Upaid Principal Balance, With no related allowance recorded	15,000		15,000		0
Recorded Investment, With an allowance recorded	0		0		0
Unpaid Principal Balance, With an allowance recorded	0		0		0
Related Allowance	0		0		0
Average Recorded Investment, With no related allowance recorded	14,000	0	10,000	0
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	0	23,000	0	48,000
Interest Income Recognized, With an allowance recorded	$ 0	$ 0	$ 0	$ 0

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5212-111524

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953550-111524

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Amount of allowance for credit losses related to recorded investment.

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Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

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Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

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Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

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Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

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Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 114

-Paragraph 20

-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.

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

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 8

-Subparagraph j(ii)

-Chapter V

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 15

-Paragraph 40

-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.

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