Loans and Allowance for Loan Losses Loans and Allowance for Loan Losses - Allowance (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) alternative	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Financing Receivable, Impaired [Line Items]
Minimum balance of adversely classified loan in which a detailed analysis is performed	$ 250
Number of alternatives for measuring impaired loans receivable | alternative	3
Balance, beginning of year	$ 19,977	$ 16,753	$ 14,576
Provision for loan losses	8,667	7,462	2,826
Losses charged off	(2,993)	(5,195)	(1,675)
Recoveries	538	957	1,026
Balance, end of period	26,189	19,977	16,753
Individually evaluated for impairment	2,044	614	858
Collectively evaluated for impairment	22,910	19,354	15,881
Ending balance	2,644,519	1,939,501	1,825,992
Individually evaluated for impairment	16,980	13,086	5,266
Collectively evaluated for impairment	$ 2,611,916	1,926,156	1,812,640
Unsecured Open-end Loans [Member]
Financing Receivable, Impaired [Line Items]
Period When Loans Are Charged Down	180 days
Other Secured Loans [Member]
Financing Receivable, Impaired [Line Items]
Period When Loans Are Charged Down	120 days
Commercial/Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	$ 16,546	12,901	11,379
Provision for loan losses	6,070	6,884	1,467
Losses charged off	(1,227)	(3,795)	(747)
Recoveries	167	556	802
Balance, end of period	21,556	16,546	12,901
Individually evaluated for impairment	1,816	586	192
Collectively evaluated for impairment	18,514	15,951	12,695
Ending balance	1,784,741	1,371,787	1,204,799
Individually evaluated for impairment	14,422	11,372	1,956
Collectively evaluated for impairment	1,756,908	1,360,156	1,199,003
Agriculture/Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	1,742	2,249	1,337
Provision for loan losses	548	153	933
Losses charged off	(93)	(662)	(30)
Recoveries	0	2	9
Balance, end of period	2,197	1,742	2,249
Individually evaluated for impairment	0	2	660
Collectively evaluated for impairment	2,197	1,740	1,589
Ending balance	367,211	213,521	212,513
Individually evaluated for impairment	32	488	1,345
Collectively evaluated for impairment	367,175	213,033	211,168
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	886	874	994
Provision for loan losses	1,447	100	113
Losses charged off	(886)	(217)	(234)
Recoveries	57	129	1
Balance, end of period	1,504	886	874
Individually evaluated for impairment	225	25	6
Collectively evaluated for impairment	1,270	861	868
Ending balance	392,526	315,123	366,823
Individually evaluated for impairment	2,360	1,026	1,752
Collectively evaluated for impairment	$ 387,961	314,097	360,825
1-4 Family residential properties
Financing Receivable, Impaired [Line Items]
Period When Loans Are Charged Down	180 days
Consumer loans
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	$ 803	693	642
Provision for loan losses	602	361	501
Losses charged off	(787)	(521)	(664)
Recoveries	314	270	214
Balance, end of period	932	803	693
Individually evaluated for impairment	3	1	0
Collectively evaluated for impairment	929	802	693
Ending balance	100,041	39,070	41,857
Individually evaluated for impairment	166	200	213
Collectively evaluated for impairment	99,872	38,870	41,644
Unallocated [Member]
Financing Receivable, Impaired [Line Items]
Balance, beginning of year	0	36	224
Provision for loan losses	0	(36)	(188)
Losses charged off	0	0	0
Recoveries	0	0	0
Balance, end of period	0	0	36
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	0	0	36
Ending balance	0	0	0
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	0	0	0
Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Allowance for Credit Losses	1,235	9	14
Financing Receivable, Net	15,623	259	8,086
Financial Asset Acquired with Credit Deterioration [Member] | Commercial/Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Allowance for Credit Losses	1,226	9	14
Financing Receivable, Net	13,411	259	3,840
Financial Asset Acquired with Credit Deterioration [Member] | Agriculture/Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Allowance for Credit Losses	0	0	0
Financing Receivable, Net	4	0	0
Financial Asset Acquired with Credit Deterioration [Member] | Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Allowance for Credit Losses	9	0	0
Financing Receivable, Net	2,205	0	4,246
Financial Asset Acquired with Credit Deterioration [Member] | Consumer loans
Financing Receivable, Impaired [Line Items]
Financing Receivable, Allowance for Credit Losses	0	0	0
Financing Receivable, Net	3	0	0
Financial Asset Acquired with Credit Deterioration [Member] | Unallocated [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Allowance for Credit Losses	0	0	0
Financing Receivable, Net	$ 0	$ 0	$ 0