Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	$ 176,090		$ 189,779
Impaired loans with related allowance - Unpaid Principal Balance	9,153		6,121
Unpaid Principal Balance	185,243		195,900
Impaired loans with no related allowance - Recorded Investment	111,706		114,253
Impaired loans with related allowance - Recorded Investment	6,126		5,502
Recorded Investment	117,832		119,755
Impaired loans with related allowance - Related Allowance	1,794		1,583
Impaired loans with no related allowance - Average Recorded Investment	112,759	56,963
Impaired loans with related allowance - Average Recorded Investment	6,150	13,857
Average Recorded Investment	118,909	70,820
Impaired loans with no related allowance - Interest Income Recognized	300	470
Impaired loans with related allowance - Interest Income Recognized	4	3
Interest Income Recognized	304	473
Commercial and industrial loans
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	35,562		35,066
Impaired loans with related allowance - Unpaid Principal Balance	1,789		1,390
Impaired loans with no related allowance - Recorded Investment	16,302		16,371
Impaired loans with related allowance - Recorded Investment	1,741		1,216
Impaired loans with related allowance - Related Allowance	902		683
Impaired loans with no related allowance - Average Recorded Investment	16,377	8,043
Impaired loans with related allowance - Average Recorded Investment	1,752	5,124
Impaired loans with no related allowance - Interest Income Recognized	21	44
Impaired loans with related allowance - Interest Income Recognized	3	3
Agricultural production financing and other loans to farmers
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	31		32
Impaired loans with no related allowance - Recorded Investment	28		30
Impaired loans with no related allowance - Average Recorded Investment	29	86
Real estate loans - Construction
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	15,184		16,109
Impaired loans with related allowance - Unpaid Principal Balance
Impaired loans with no related allowance - Recorded Investment	10,327		10,625
Impaired loans with related allowance - Recorded Investment
Impaired loans with related allowance - Related Allowance
Impaired loans with no related allowance - Average Recorded Investment	10,440	3,936
Impaired loans with related allowance - Average Recorded Investment		915
Impaired loans with no related allowance - Interest Income Recognized	28	19
Real estate loans - Commercial and farm land
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	115,745		128,073
Impaired loans with related allowance - Unpaid Principal Balance	7,364		4,657
Impaired loans with no related allowance - Recorded Investment	80,957		83,033
Impaired loans with related allowance - Recorded Investment	4,385		4,215
Impaired loans with related allowance - Related Allowance	892		894
Impaired loans with no related allowance - Average Recorded Investment	81,617	39,228
Impaired loans with related allowance - Average Recorded Investment	4,398	5,428
Impaired loans with no related allowance - Interest Income Recognized	243	382
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	6,196		6,746
Impaired loans with related allowance - Unpaid Principal Balance			74
Impaired loans with no related allowance - Recorded Investment	3,948		3,910
Impaired loans with related allowance - Recorded Investment			71
Impaired loans with related allowance - Related Allowance			6
Impaired loans with no related allowance - Average Recorded Investment	4,146	4,737
Impaired loans with related allowance - Average Recorded Investment		2,390
Impaired loans with no related allowance - Interest Income Recognized	8	22
Real estate loans - Home equity
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance - Unpaid Principal Balance	3,332		3,299
Impaired loans with no related allowance - Recorded Investment	142		112
Impaired loans with no related allowance - Average Recorded Investment	144	923
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	40		454
Impaired loans with no related allowance - Recorded Investment	2		172
Impaired loans with no related allowance - Average Recorded Investment	$ 6	$ 10