Fair Value Disclosures - Assets, Liabilities and Off-balance Sheet Items Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Assets:
Held-to-maturity securities	$ 105,642	$ 55,320
Other real estate owned	1,433	1,843
Total assets	1,801		$ 2,014
Deposits:
Time deposits	671,483	574,749
Subordinated notes	94,514	94,331
Fair Value [Member]
Assets:
Cash and short-term interest-earning assets	84,110	75,409
Held-to-maturity securities	105,642	55,320
Loans held for sale	114	1,676
Net loans and leases held for investment	3,794,987	3,547,451
Servicing rights	11,935	10,046
Total assets	3,996,788	3,689,902
Deposits:
Demand and savings deposits, non-maturity	3,148,565	2,980,170
Time deposits	661,806	574,737
Total deposits	3,810,371	3,554,907
Short-term borrowings	86,765	105,431
Long-term debt	142,862	156,834
Subordinated notes	96,063	98,075
Total liabilities	4,136,061	3,915,247
Off-Balance-Sheet:
Commitments to extend credit	(2,508)	(2,414)
Fair Value [Member] | Level 1 [Member]
Assets:
Cash and short-term interest-earning assets	84,110	75,409
Held-to-maturity securities	0	0
Loans held for sale	0	0
Net loans and leases held for investment	0	0
Servicing rights	0	0
Total assets	84,110	75,409
Deposits:
Demand and savings deposits, non-maturity	3,148,565	2,980,170
Time deposits	0	0
Total deposits	3,148,565	2,980,170
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated notes	0	0
Total liabilities	3,148,565	2,980,170
Off-Balance-Sheet:
Commitments to extend credit	0	0
Fair Value [Member] | Level 2 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	105,642	55,320
Loans held for sale	114	1,676
Net loans and leases held for investment	0	0
Servicing rights	0	0
Total assets	105,756	56,996
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	661,806	574,737
Total deposits	661,806	574,737
Short-term borrowings	86,765	105,431
Long-term debt	142,862	156,834
Subordinated notes	96,063	98,075
Total liabilities	987,496	935,077
Off-Balance-Sheet:
Commitments to extend credit	(2,508)	(2,414)
Fair Value [Member] | Level 3 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	0	0
Loans held for sale	0	0
Net loans and leases held for investment	3,794,987	3,547,451
Servicing rights	11,935	10,046
Total assets	3,806,922	3,557,497
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	0	0
Total deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated notes	0	0
Total liabilities	0	0
Off-Balance-Sheet:
Commitments to extend credit	0	0
Carrying Amount [Member]
Assets:
Cash and short-term interest-earning assets	84,110	75,409
Held-to-maturity securities	108,142	55,564
Federal Home Loan Bank, Federal Reserve Bank and other stock	33,071	27,204
Loans held for sale	106	1,642
Net loans and leases held for investment	3,808,073	3,566,953
Servicing rights	6,715	6,573
Total assets	4,040,217	3,733,345
Deposits:
Demand and savings deposits, non-maturity	3,148,565	2,980,170
Time deposits	671,483	574,749
Total deposits	3,820,048	3,554,919
Short-term borrowings	86,765	105,431
Long-term debt	145,430	155,828
Subordinated notes	94,514	94,331
Total liabilities	4,146,757	3,910,509
Off-Balance-Sheet:
Commitments to extend credit	0	0
Fair Value Measured on Recurring Basis [Member]
Assets:
Net loans and leases held for investment	1,801	1,958
Total assets	341,861	401,077
Deposits:
Total liabilities	354	425
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member]
Assets:
Net loans and leases held for investment	0	0
Total assets	2,264	7,061
Deposits:
Total liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member]
Assets:
Net loans and leases held for investment	0	0
Total assets	311,389	364,072
Deposits:
Total liabilities	20	50
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member]
Assets:
Net loans and leases held for investment	1,801	1,958
Total assets	28,208	29,944
Deposits:
Total liabilities	$ 334	$ 375