Allowance for Credit Losses, Aging Analysis of Loan Portfolio by the Time Past Due (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	$ 0	$ 0
Nonaccrual	3,074	2,156
Total Past Due	3,084	3,159
Current	2,174,517	1,993,200
Total Loans & Leases	2,177,601	1,996,359
Interest income forgone on nonaccrual loans	127	109	$ 92
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10	809
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	194
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	0	19
Total Past Due	0	724
Current	668,046	602,926
Total Loans & Leases	668,046	603,650
Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	705
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	1,304	0
Total Past Due	1,304	0
Current	466,381	424,034
Total Loans & Leases	467,685	424,034
Agricultural Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	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
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	0
Current	176,462	151,974
Total Loans & Leases	176,462	151,974
Real Estate Construction [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	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
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	95	65
Total Past Due	95	356
Current	242,152	206,049
Total Loans & Leases	242,247	206,405
Residential 1st Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	97
Residential 1st Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	194
Home Equity Lines and Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	0	538
Total Past Due	0	538
Current	31,625	32,518
Total Loans & Leases	31,625	33,056
Home Equity Lines and Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Home Equity Lines and Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	243	0
Total Past Due	243	0
Current	295,082	293,966
Total Loans & Leases	295,325	293,966
Agricultural [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Agricultural [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	1,425	1,524
Total Past Due	1,425	1,524
Current	216,152	209,280
Total Loans & Leases	217,577	210,804
Commercial [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Commercial [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Consumer & Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	7	10
Total Past Due	17	17
Current	6,896	6,575
Total Loans & Leases	6,913	6,592
Consumer & Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10	7
Consumer & Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	0
Current	71,721	65,878
Total Loans & Leases	71,721	65,878
Leases [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Leases [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0