Allowance for Credit Losses - Impaired Loans (Details) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	$ 7,446,000		$ 7,446,000		$ 2,875,000
Upaid Principal Balance, With no related allowance recorded	9,189,000		9,189,000		3,722,000
Recorded Investment, With an allowance recorded	8,511,000		8,511,000		14,230,000
Unpaid Principal Balance, With an allowance recorded	9,112,000		9,112,000		15,336,000
Related Allowance	871,000		871,000		510,000
Total Recorded Investment	15,957,000		15,957,000		17,105,000
Total Unpaid Principal Balance	18,301,000		18,301,000		19,058,000
Average Recorded Investment, With no related allowance recorded	7,511,000	8,935,000	7,447,000	9,308,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	8,749,000	8,741,000	8,963,000	8,029,000
Interest Income Recognized, With an allowance recorded	147,000	150,000	265,000	320,000
Average Recorded Investment, Total	16,260,000	17,676,000	16,410,000	17,337,000
Interest Income Recognized, Total	147,000	150,000	265,000	320,000
Forgone interest on nonaccrual loans	216,000	171,000	378,000	345,000
Commercial
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	1,339,000		1,339,000		2,405,000
Unpaid Principal Balance, With an allowance recorded	1,355,000		1,355,000		2,405,000
Related Allowance	410,000		410,000		40,000
Average Recorded Investment, With no related allowance recorded	0	1,144,000	0	1,412,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	1,589,000	1,473,000	1,803,000	1,511,000
Interest Income Recognized, With an allowance recorded	32,000	56,000	65,000	127,000
Commercial and industrial
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	1,339,000		1,339,000		2,405,000
Unpaid Principal Balance, With an allowance recorded	1,355,000		1,355,000		2,405,000
Related Allowance	410,000		410,000		40,000
Average Recorded Investment, With no related allowance recorded	0	1,144,000	0	1,412,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	1,589,000	1,473,000	1,803,000	1,511,000
Interest Income Recognized, With an allowance recorded	32,000	56,000	65,000	127,000
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	5,741,000		5,741,000		1,352,000
Upaid Principal Balance, With no related allowance recorded	7,107,000		7,107,000		1,888,000
Recorded Investment, With an allowance recorded	6,992,000		6,992,000		11,516,000
Unpaid Principal Balance, With an allowance recorded	7,572,000		7,572,000		12,608,000
Related Allowance	408,000		408,000		465,000
Average Recorded Investment, With no related allowance recorded	5,792,000	6,033,000	5,755,000	6,436,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	7,017,000	6,868,000	7,014,000	6,164,000
Interest Income Recognized, With an allowance recorded	115,000	94,000	200,000	193,000
Owner occupied
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	198,000		198,000		0
Upaid Principal Balance, With no related allowance recorded	235,000		235,000		0
Recorded Investment, With an allowance recorded	1,318,000		1,318,000		1,575,000
Unpaid Principal Balance, With an allowance recorded	1,482,000		1,482,000		1,733,000
Related Allowance	67,000		67,000		165,000
Average Recorded Investment, With no related allowance recorded	204,000	1,022,000	137,000	625,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	1,322,000	0	1,402,000	0
Interest Income Recognized, With an allowance recorded	30,000	0	30,000	0
Real estate construction and other land loans
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	5,389,000		5,389,000		1,352,000
Upaid Principal Balance, With no related allowance recorded	6,718,000		6,718,000		1,888,000
Recorded Investment, With an allowance recorded	5,674,000		5,674,000		9,941,000
Unpaid Principal Balance, With an allowance recorded	6,090,000		6,090,000		10,875,000
Related Allowance	341,000		341,000		300,000
Average Recorded Investment, With no related allowance recorded	5,432,000	5,011,000	5,488,000	5,811,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	5,695,000	6,868,000	5,612,000	6,164,000
Interest Income Recognized, With an allowance recorded	85,000	94,000	170,000	193,000
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Investment, With no related allowance recorded	154,000		154,000		0
Upaid Principal Balance, With no related allowance recorded	154,000		154,000		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	156,000	0	130,000	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
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	1,705,000		1,705,000		1,523,000
Upaid Principal Balance, With no related allowance recorded	2,082,000		2,082,000		1,834,000
Recorded Investment, With an allowance recorded	180,000		180,000		309,000
Unpaid Principal Balance, With an allowance recorded	185,000		185,000		323,000
Related Allowance	53,000		53,000		5,000
Average Recorded Investment, With no related allowance recorded	1,719,000	1,758,000	1,692,000	1,460,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	143,000	400,000	146,000	354,000
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	1,705,000		1,705,000		1,523,000
Upaid Principal Balance, With no related allowance recorded	2,082,000		2,082,000		1,834,000
Recorded Investment, With an allowance recorded	180,000		180,000		309,000
Unpaid Principal Balance, With an allowance recorded	185,000		185,000		323,000
Related Allowance	53,000		53,000		5,000
Average Recorded Investment, With no related allowance recorded	1,719,000	1,758,000	1,692,000	1,460,000
Interest Income Recognized, With no related allowance recorded	0	0	0	0
Average Recorded Investment, With an allowance recorded	143,000	352,000	146,000	294,000
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	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	48,000	0	60,000
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

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

-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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- Definition

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 average investment of 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 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 average investment of impaired financing receivables for which there is a 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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-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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