Loans & Leases and Allowance for Credit Losses, Aging Analysis of Loan Portfolio by the Time Past Due (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	$ 0	$ 0	$ 0
Nonaccrual	4	3,074	3,075
Total Past Due	23	3,084	4,063
Current	2,216,756	2,174,517	2,075,607
Total Loans & Leases	2,216,779	2,177,601	2,079,670
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16	10	5
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3	0	983
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	998
Total Past Due	0	0	998
Current	683,037	668,046	626,116
Total Loans & Leases	683,037	668,046	627,114
Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	1,304	322
Total Past Due	0	1,304	1,305
Current	470,738	466,381	438,667
Total Loans & Leases	470,738	467,685	439,972
Agricultural Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Agricultural Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	983
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	162,167	176,462	175,045
Total Loans & Leases	162,167	176,462	175,045
Real Estate Construction [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Real Estate Construction [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	95	55
Total Past Due	0	95	55
Current	257,920	242,152	238,321
Total Loans & Leases	257,920	242,247	238,376
Residential 1st Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Residential 1st Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	33,350	31,625	32,513
Total Loans & Leases	33,350	31,625	32,513
Home Equity Lines & Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Home Equity Lines & Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	243	243
Total Past Due	0	243	243
Current	259,127	295,082	274,461
Total Loans & Leases	259,127	295,325	274,704
Agricultural [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Agricultural [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	1,425	1,450
Total Past Due	3	1,425	1,450
Current	257,948	216,152	212,636
Total Loans & Leases	257,951	217,577	214,086
Commercial [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Commercial [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3	0	0
Consumer & Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	4	7	7
Total Past Due	20	17	12
Current	7,292	6,896	6,963
Total Loans & Leases	7,312	6,913	6,975
Consumer & Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16	10	5
Consumer & Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	85,177	71,721	70,885
Total Loans & Leases	85,177	71,721	70,885
Leases [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0	0
Leases [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0	$ 0