Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unpaid Principal Balance
Impaired loans with no related allowance	$ 134,581	$ 158,563	$ 189,779
Impaired loans with related allowance	7,953	16,703	6,121
Total Impaired Loans	142,534	175,266	195,900
Recorded Investment
Impaired loans with no related allowance	90,975	102,793	114,253
Impaired loans with related allowance	6,552	13,430	5,502
Total Impaired Loans	97,527	116,223	119,755
Related Allowance	1,842	2,769	1,583
Average Recorded Investment
Impaired loans with no related allowance	96,423	106,807	119,561
Impaired loans with related allowance	6,945	15,764	5,607
Total Impaired Loans	103,368	122,571	125,168
Interest Income Recognized
Impaired loans with no related allowance	4,217	4,297	2,048
Impaired loans with related allowance	38	65	18
Total Impaired Loans	4,255	4,362	2,066
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	22,151	35,514	35,066
Impaired loans with related allowance	3,043	1,766	1,390
Recorded Investment
Impaired loans with no related allowance	11,669	18,029	16,371
Impaired loans with related allowance	2,690	1,684	1,216
Related Allowance	1,247	1,055	683
Average Recorded Investment
Impaired loans with no related allowance	12,578	18,711	19,209
Impaired loans with related allowance	2,752	1,721	1,240
Interest Income Recognized
Impaired loans with no related allowance	488	362	192
Impaired loans with related allowance	38	40	9
Agriculture production financing and other loans to farmers
Unpaid Principal Balance
Impaired loans with no related allowance	370	26	32
Impaired loans with related allowance	466	6,777
Recorded Investment
Impaired loans with no related allowance	361	22	30
Impaired loans with related allowance	466	5,777
Related Allowance	30	400
Average Recorded Investment
Impaired loans with no related allowance	439	26	32
Impaired loans with related allowance	$ 538	8,044
Interest Income Recognized
Impaired loans with related allowance		1
Construction
Unpaid Principal Balance
Impaired loans with no related allowance	$ 4,551	12,956	16,109
Recorded Investment
Impaired loans with no related allowance	2,336	9,318	10,625
Average Recorded Investment
Impaired loans with no related allowance	3,662	9,837	11,621
Interest Income Recognized
Impaired loans with no related allowance	157	427	117
Commercial and farmland
Unpaid Principal Balance
Impaired loans with no related allowance	95,930	95,856	128,073
Impaired loans with related allowance	2,144	7,159	4,657
Recorded Investment
Impaired loans with no related allowance	69,024	68,187	83,033
Impaired loans with related allowance	1,933	4,971	4,215
Related Allowance	392	1,120	894
Average Recorded Investment
Impaired loans with no related allowance	71,569	70,844	84,057
Impaired loans with related allowance	1,868	4,999	4,291
Interest Income Recognized
Impaired loans with no related allowance	$ 3,328	3,389	1,663
Impaired loans with related allowance		24	9
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	$ 11,262	10,591	6,746
Impaired loans with related allowance	2,300	1,001	74
Recorded Investment
Impaired loans with no related allowance	7,338	6,839	3,910
Impaired loans with related allowance	1,463	998	71
Related Allowance	173	194	6
Average Recorded Investment
Impaired loans with no related allowance	7,926	6,987	4,236
Impaired loans with related allowance	1,787	1,000	76
Interest Income Recognized
Impaired loans with no related allowance	$ 244	$ 119	$ 75
Impaired loans with related allowance
Home equity
Unpaid Principal Balance
Impaired loans with no related allowance	$ 297	$ 3,590	$ 3,299
Recorded Investment
Impaired loans with no related allowance	247	398	112
Average Recorded Investment
Impaired loans with no related allowance	$ 249	$ 402	$ 225
Interest Income Recognized
Impaired loans with no related allowance
Other commercial loans
Unpaid Principal Balance
Impaired loans with no related allowance	$ 20	$ 30	$ 454
Recorded Investment
Impaired loans with no related allowance			172
Average Recorded Investment
Impaired loans with no related allowance			181
Interest Income Recognized
Impaired loans with no related allowance			$ 1