Fair Value Disclosures - Assets, Liabilities and Off-balance Sheet Items Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Assets:
Held-to-maturity securities	$ 182,376	$ 194,886
Total assets	221		$ 349
Deposits:
Time deposits	556,219	606,010
Subordinated notes	193,413	94,818
Fair Value [Member]
Assets:
Cash and short-term interest-earning assets	387,676	125,128
Held-to-maturity securities	182,376	194,886
Loans held for sale	14,612	5,560
Net loans and leases held for investment	5,253,500	4,309,208
Servicing rights	6,404	9,340
Total assets	5,844,568	4,644,122
Deposits:
Demand and savings deposits, non-maturity	4,655,384	3,754,065
Time deposits	567,257	609,387
Total deposits	5,222,641	4,363,452
Short-term borrowings	17,681	18,680
Long-term debt	209,494	151,343
Subordinated notes	199,473	96,663
Total liabilities	5,649,289	4,630,138
Fair Value [Member] | Level 1 [Member]
Assets:
Cash and short-term interest-earning assets	387,676	125,128
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	387,676	125,128
Deposits:
Demand and savings deposits, non-maturity	4,655,384	3,754,065
Time deposits	0	0
Total deposits	4,655,384	3,754,065
Short-term borrowings	0	0
Long-term debt	0	0
Subordinated notes	0	0
Total liabilities	4,655,384	3,754,065
Fair Value [Member] | Level 2 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	182,376	194,886
Loans held for sale	14,612	5,560
Net loans and leases held for investment	0	0
Servicing rights	0	0
Total assets	196,988	200,446
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	567,257	609,387
Total deposits	567,257	609,387
Short-term borrowings	17,681	18,680
Long-term debt	209,494	151,343
Subordinated notes	199,473	96,663
Total liabilities	993,905	876,073
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	5,253,500	4,309,208
Servicing rights	6,404	9,340
Total assets	5,259,904	4,318,548
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
Carrying Amount [Member]
Assets:
Cash and short-term interest-earning assets	387,676	125,128
Held-to-maturity securities	176,817	192,052
Federal Home Loan Bank, Federal Reserve Bank and other stock	29,723	28,254
Loans held for sale	14,465	5,504
Net loans and leases held for investment	5,091,090	4,314,893
Servicing rights	6,279	6,626
Total assets	5,706,050	4,672,457
Deposits:
Demand and savings deposits, non-maturity	4,655,384	3,754,065
Time deposits	556,219	606,010
Total deposits	5,211,603	4,360,075
Short-term borrowings	17,681	18,680
Long-term debt	205,010	150,098
Subordinated notes	193,413	94,818
Total liabilities	$ 5,627,707	$ 4,623,671