Loans (Impaired Loans Not Covered by Loss Share Agreements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Unpaid Principal Balance
Impaired loans with a related allowance	$ 17,005	$ 19,958
Impaired loans without a related allowance	69,265	64,121
Total impaired loans held to maturity	86,270	84,079
Loan Balance
Impaired loans with a related allowance	16,995	18,101
Impaired loans without a related allowance	64,801	60,367
Total impaired loans held to maturity	81,796	78,468
Impaired loans, related allowance recorded	7,554	4,755
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	15,399	22,949
Impaired loans without a related allowance	66,900	62,296
Total impaired loans held to maturity	82,299	85,245
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	101	129
Impaired loans without a related allowance	958	1,029
Total loans held to maturity	1,059	1,158
Commercial
Unpaid Principal Balance
Impaired loans with a related allowance	13,267	14,217
Impaired loans without a related allowance	27,194	20,486
Total impaired loans held to maturity	40,461	34,703
Loan Balance
Impaired loans with a related allowance	13,257	12,360
Impaired loans without a related allowance	25,333	18,760
Total impaired loans held to maturity	38,590	31,120
Impaired loans, related allowance recorded	5,951	2,379
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	9,162	15,086
Impaired loans without a related allowance	23,052	22,734
Total impaired loans held to maturity	32,214	37,820
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	58	73
Impaired loans without a related allowance	548	679
Total loans held to maturity	606	752
Commercial | Commercial
Unpaid Principal Balance
Impaired loans with a related allowance	12,376	2,292
Impaired loans without a related allowance	13,616	6,243
Total impaired loans held to maturity	25,992	8,535
Loan Balance
Impaired loans with a related allowance	12,366	2,292
Impaired loans without a related allowance	11,836	5,123
Total impaired loans held to maturity	24,202	7,415
Impaired loans, related allowance recorded	5,733	1,613
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	4,741	3,607
Impaired loans without a related allowance	10,052	2,586
Total impaired loans held to maturity	14,793	6,193
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	33	39
Impaired loans without a related allowance	299	165
Total loans held to maturity	332	204
Commercial | Commercial real estate
Unpaid Principal Balance
Impaired loans with a related allowance	891	11,925
Impaired loans without a related allowance	13,578	14,243
Total impaired loans held to maturity	14,469	26,168
Loan Balance
Impaired loans with a related allowance	891	10,068
Impaired loans without a related allowance	13,497	13,637
Total impaired loans held to maturity	14,388	23,705
Impaired loans, related allowance recorded	218	766
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	4,421	11,479
Impaired loans without a related allowance	13,000	20,148
Total impaired loans held to maturity	17,421	31,627
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	25	34
Impaired loans without a related allowance	249	514
Total loans held to maturity	274	548
Agricultural and agricultural real estate
Unpaid Principal Balance
Impaired loans with a related allowance	1,718	1,539
Impaired loans without a related allowance	16,836	13,793
Total impaired loans held to maturity	18,554	15,332
Loan Balance
Impaired loans with a related allowance	1,718	1,539
Impaired loans without a related allowance	14,233	11,765
Total impaired loans held to maturity	15,951	13,304
Impaired loans, related allowance recorded	686	546
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	2,165	3,437
Impaired loans without a related allowance	14,781	9,654
Total impaired loans held to maturity	16,946	13,091
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	2	0
Impaired loans without a related allowance	5	0
Total loans held to maturity	7	0
Residential real estate
Unpaid Principal Balance
Impaired loans with a related allowance	647	1,568
Impaired loans without a related allowance	19,604	25,573
Total impaired loans held to maturity	20,251	27,141
Loan Balance
Impaired loans with a related allowance	647	1,568
Impaired loans without a related allowance	19,604	25,573
Total impaired loans held to maturity	20,251	27,141
Impaired loans, related allowance recorded	168	430
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	1,138	2,056
Impaired loans without a related allowance	23,950	26,024
Total impaired loans held to maturity	25,088	28,080
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	12	15
Impaired loans without a related allowance	308	277
Total loans held to maturity	320	292
Consumer
Unpaid Principal Balance
Impaired loans with a related allowance	1,373	2,634
Impaired loans without a related allowance	5,631	4,269
Total impaired loans held to maturity	7,004	6,903
Loan Balance
Impaired loans with a related allowance	1,373	2,634
Impaired loans without a related allowance	5,631	4,269
Total impaired loans held to maturity	7,004	6,903
Impaired loans, related allowance recorded	749	1,400
Year-to-Date Avg. Loan Balance
Impaired loans with a related allowance	2,934	2,370
Impaired loans without a related allowance	5,117	3,884
Total impaired loans held to maturity	8,051	6,254
Year-to-Date Interest Income Recognized
Impaired loans with a related allowance	29	41
Impaired loans without a related allowance	97	73
Total loans held to maturity	$ 126	$ 114