Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	$ 136,861		$ 158,563
Impaired loans with related allowance - Unpaid Principal Balance	12,896		16,703
Unpaid Principal Balance	149,757		175,266
Impaired loans with no related allowance - Recorded Investment	93,646		102,793
Impaired loans with related allowance - Recorded Investment	10,904		13,430
Recorded Investment	104,550		116,223
Impaired financing receivable, allowance	4,556	1,794	2,769
Impaired loans with no related allowance - Average Recorded Investment	103,092	112,759
Impaired loans with related allowance - Average Recorded Investment	13,244	6,150
Average Recorded Investment	116,336	118,909
Impaired loans with no related allowance - Interest Income Recognized	1,172	300
Impaired loans with related allowance - Interest Income Recognized	10	4
Interest Income Recognized	1,182	304
Commercial and industrial loans
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	27,308		35,514
Impaired loans with related allowance - Unpaid Principal Balance	4,434		1,766
Impaired loans with no related allowance - Recorded Investment	13,460		18,029
Impaired loans with related allowance - Recorded Investment	4,376		1,684
Impaired financing receivable, allowance	2,461		1,055
Impaired loans with no related allowance - Average Recorded Investment	16,150	16,377
Impaired loans with related allowance - Average Recorded Investment	4,379	1,752
Impaired loans with no related allowance - Interest Income Recognized	139	21
Impaired loans with related allowance - Interest Income Recognized	10	3
Agricultural production financing and other loans to farmers
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	307		26
Impaired loans with related allowance - Unpaid Principal Balance	3,415		6,777
Impaired loans with no related allowance - Recorded Investment	302		22
Impaired loans with related allowance - Recorded Investment	1,676		5,777
Impaired financing receivable, allowance	239		400
Impaired loans with no related allowance - Average Recorded Investment	303	29
Impaired loans with related allowance - Average Recorded Investment	3,991
Real estate loans - Construction
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	10,811		12,956
Impaired loans with no related allowance - Recorded Investment	7,856		9,318
Impaired loans with no related allowance - Average Recorded Investment	8,542	10,440
Impaired loans with no related allowance - Interest Income Recognized	104	28
Real estate loans - Commercial and farmland
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	88,069		95,856
Impaired loans with related allowance - Unpaid Principal Balance	3,171		7,159
Impaired loans with no related allowance - Recorded Investment	65,281		68,187
Impaired loans with related allowance - Recorded Investment	3,093		4,971
Impaired financing receivable, allowance	1,302		1,120
Impaired loans with no related allowance - Average Recorded Investment	69,036	81,617
Impaired loans with related allowance - Average Recorded Investment	3,113	4,398
Impaired loans with no related allowance - Interest Income Recognized	878	243
Impaired loans with related allowance - Interest Income Recognized		1
Real estate loans - Residential
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	9,792		10,591
Impaired loans with related allowance - Unpaid Principal Balance	1,876		1,001
Impaired loans with no related allowance - Recorded Investment	6,273		6,839
Impaired loans with related allowance - Recorded Investment	1,759		998
Impaired financing receivable, allowance	554		194
Impaired loans with no related allowance - Average Recorded Investment	8,528	4,146
Impaired loans with related allowance - Average Recorded Investment	1,761
Impaired loans with no related allowance - Interest Income Recognized	48	8
Impaired loans with related allowance - Interest Income Recognized
Real estate loans - Home equity
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	546		3,590
Impaired loans with no related allowance - Recorded Investment	474		398
Impaired loans with no related allowance - Average Recorded Investment	533	144
Impaired loans with no related allowance - Interest Income Recognized	3
Other loans
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	28		30
Impaired loans with no related allowance - Recorded Investment
Impaired loans with no related allowance - Average Recorded Investment		$ 6

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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=35738203&loc=d3e5212-111524

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-Topic 310

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