Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	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]
Impaired loans with no related allowance - Unpaid Principal Balance	$ 78,810		$ 78,810		$ 109,594
Impaired loans with related allowance - Unpaid Principal Balance	19,189		19,189		12,918
Unpaid Principal Balance	97,999		97,999		122,512
Impaired loans with no related allowance - Recorded Investment	47,524		47,524		67,333
Impaired loans with related allowance - Recorded Investment	15,465		15,465		11,846
Recorded Investment	62,989		62,989		79,179
Impaired loans with related allowance - Related Allowance	4,548		4,548		4,243
Impaired loans with no related allowance - Average Recorded Investment	48,213	67,077	49,082	70,429
Impaired loans with related allowance - Average Recorded Investment	15,885	18,423	16,456	18,570
Average Recorded Investment	64,098	85,500	65,538	88,999
Impaired loans with no related allowance - Interest Income Recognized	454	388	904	700
Impaired loans with related allowance - Interest Income Recognized	3	75	5	148
Interest Income Recognized	457	463	909	848
Commercial and industrial loans
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	17,836		17,836		28,532
Impaired loans with related allowance - Unpaid Principal Balance	7,193		7,193		4,415
Impaired loans with no related allowance - Recorded Investment	5,556		5,556		11,730
Impaired loans with related allowance - Recorded Investment	5,306		5,306		4,155
Impaired loans with related allowance - Related Allowance	1,476		1,476		1,628
Impaired loans with no related allowance - Average Recorded Investment	5,864	11,411	6,138	12,418
Impaired loans with related allowance - Average Recorded Investment	5,669	6,111	6,138	6,136
Impaired loans with no related allowance - Interest Income Recognized	35	39	69	64
Impaired loans with related allowance - Interest Income Recognized	3	11	5	21
Agriculture production financing and other loans to farmers
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	34		34
Impaired loans with no related allowance - Recorded Investment	33		33
Impaired loans with no related allowance - Average Recorded Investment	33		33
Real estate loans - Construction
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	4,540		4,540		9,787
Impaired loans with related allowance - Unpaid Principal Balance	961		961		1,202
Impaired loans with no related allowance - Recorded Investment	3,053		3,053		5,164
Impaired loans with related allowance - Recorded Investment	599		599		1,058
Impaired loans with related allowance - Related Allowance	74		74		105
Impaired loans with no related allowance - Average Recorded Investment	3,060	8,040	3,070	8,581
Impaired loans with related allowance - Average Recorded Investment	599	1,931	599	1,936
Impaired loans with no related allowance - Interest Income Recognized	19	16	38	29
Impaired loans with related allowance - Interest Income Recognized
Real estate loans - Commercial and farm land
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	44,620		44,620		58,173
Impaired loans with related allowance - Unpaid Principal Balance	10,249		10,249		5,579
Impaired loans with no related allowance - Recorded Investment	32,658		32,658		43,204
Impaired loans with related allowance - Recorded Investment	9,177		9,177		5,182
Impaired loans with related allowance - Related Allowance	2,823		2,823		2,460
Impaired loans with no related allowance - Average Recorded Investment	32,932	41,084	33,192	42,615
Impaired loans with related allowance - Average Recorded Investment	9,227	8,369	9,323	8,505
Impaired loans with no related allowance - Interest Income Recognized	382	315	760	575
Impaired loans with related allowance - Interest Income Recognized		45		89
Real estate loans - Residential
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	8,228		8,228		8,820
Impaired loans with related allowance - Unpaid Principal Balance	465		465		1,722
Impaired loans with no related allowance - Recorded Investment	5,968		5,968		6,215
Impaired loans with related allowance - Recorded Investment	235		235		1,451
Impaired loans with related allowance - Related Allowance	29		29		50
Impaired loans with no related allowance - Average Recorded Investment	6,067	5,815	6,372	6,072
Impaired loans with related allowance - Average Recorded Investment	238	2,012	240	1,993
Impaired loans with no related allowance - Interest Income Recognized	18	15	37	26
Impaired loans with related allowance - Interest Income Recognized		19		38
Real estate loans - Home equity
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	3,412		3,412		4,199
Impaired loans with no related allowance - Recorded Investment	226		226		1,006
Impaired loans with no related allowance - Average Recorded Investment	226	570	245	585
Impaired loans with no related allowance - Interest Income Recognized		3		6
Individuals' loans for household and other personal expenditures
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Average Recorded Investment		139		139
Impaired loans with no related allowance - Interest Income Recognized
Other Loans
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	140		140		83
Impaired loans with related allowance - Unpaid Principal Balance	321		321
Impaired loans with no related allowance - Recorded Investment	30		30		14
Impaired loans with related allowance - Recorded Investment	148		148
Impaired loans with related allowance - Related Allowance	146		146
Impaired loans with no related allowance - Average Recorded Investment	31	18	32	19
Impaired loans with related allowance - Average Recorded Investment	152		156
Impaired loans with no related allowance - Interest Income Recognized
Impaired loans with related allowance - Interest Income Recognized

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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

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-SubTopic 10

-Section 50

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