Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Unpaid Principal Balance
Impaired loans with no related allowance	$ 100,416	$ 134,581	$ 158,563
Impaired loans with related allowance	4,963	7,953	16,703
Total Impaired Loans	105,379	142,534	175,266
Recorded Investment
Impaired loans with no related allowance	68,371	90,975	102,793
Impaired loans with related allowance	3,679	6,552	13,430
Total Impaired Loans	72,050	97,527	116,223
Related Allowance	612	1,842	2,769
Average Recorded Investment
Impaired loans with no related allowance	74,592	96,423	106,807
Impaired loans with related allowance	3,718	6,945	15,764
Total Impaired Loans	78,310	103,368	122,571
Interest Income Recognized
Impaired loans with no related allowance	3,905	4,217	4,297
Impaired loans with related allowance		38	65
Total Impaired Loans	3,905	4,255	4,362
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	17,645	22,151	35,514
Impaired loans with related allowance		3,043	1,766
Recorded Investment
Impaired loans with no related allowance	10,074	11,669	18,029
Impaired loans with related allowance		2,690	1,684
Related Allowance		1,247	1,055
Average Recorded Investment
Impaired loans with no related allowance	13,393	12,578	18,711
Impaired loans with related allowance		2,752	1,721
Interest Income Recognized
Impaired loans with no related allowance	499	488	362
Impaired loans with related allowance		38	40
Agriculture production financing and other loans to farmers
Unpaid Principal Balance
Impaired loans with no related allowance	757	370	26
Impaired loans with related allowance	660	466	6,777
Recorded Investment
Impaired loans with no related allowance	680	361	22
Impaired loans with related allowance	660	466	5,777
Related Allowance	36	30	400
Average Recorded Investment
Impaired loans with no related allowance	750	439	26
Impaired loans with related allowance	691	538	8,044
Interest Income Recognized
Impaired loans with no related allowance	3
Impaired loans with related allowance			1
Construction
Unpaid Principal Balance
Impaired loans with no related allowance	5,946	4,551	12,956
Recorded Investment
Impaired loans with no related allowance	3,178	2,336	9,318
Average Recorded Investment
Impaired loans with no related allowance	3,255	3,662	9,837
Interest Income Recognized
Impaired loans with no related allowance	258	157	427
Commercial and farmland
Unpaid Principal Balance
Impaired loans with no related allowance	67,936	95,930	95,856
Impaired loans with related allowance	4,238	2,144	7,159
Recorded Investment
Impaired loans with no related allowance	49,731	69,024	68,187
Impaired loans with related allowance	2,985	1,933	4,971
Related Allowance	553	392	1,120
Average Recorded Investment
Impaired loans with no related allowance	51,740	71,569	70,844
Impaired loans with related allowance	2,989	1,868	4,999
Interest Income Recognized
Impaired loans with no related allowance	2,978	3,328	3,389
Impaired loans with related allowance			24
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	8,039	11,262	10,591
Impaired loans with related allowance	65	2,300	1,001
Recorded Investment
Impaired loans with no related allowance	4,664	7,338	6,839
Impaired loans with related allowance	34	1,463	998
Related Allowance	23	173	194
Average Recorded Investment
Impaired loans with no related allowance	5,410	7,926	6,987
Impaired loans with related allowance	38	1,787	1,000
Interest Income Recognized
Impaired loans with no related allowance	167	244	119
Impaired loans with related allowance
Home equity
Unpaid Principal Balance
Impaired loans with no related allowance	82	297	3,590
Recorded Investment
Impaired loans with no related allowance	44	247	398
Average Recorded Investment
Impaired loans with no related allowance	44	249	402
Interest Income Recognized
Impaired loans with no related allowance
Other commercial loans
Unpaid Principal Balance
Impaired loans with no related allowance	11	20	30
Recorded Investment
Impaired loans with no related allowance
Average Recorded Investment
Impaired loans with no related allowance
Interest Income Recognized
Impaired loans with no related allowance