Loans and Allowance for Loan Losses - Impaired Loans, Net of Government Guarantees and Excluding Loans Acquired, Segregated by Class of Loans (Details) - Loans, Excluding Acquired Loans - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2020
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		$ 90,639
Recorded Investment With No Allowance		33,043
Recorded Investment With Allowance		35,889
Total Recorded Investment		68,932
Related Allowance		5,747
Average Investment in Impaired Loans	$ 48,675
Interest Income Recognized	375
Consumer
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		1,919
Recorded Investment With No Allowance		1,760
Recorded Investment With Allowance		0
Total Recorded Investment		1,760
Related Allowance		0
Average Investment in Impaired Loans	2,174
Interest Income Recognized	43
Consumer | Credit cards
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		382
Recorded Investment With No Allowance		382
Recorded Investment With Allowance		0
Total Recorded Investment		382
Related Allowance		0
Average Investment in Impaired Loans	317
Interest Income Recognized	30
Consumer | Other consumer
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		1,537
Recorded Investment With No Allowance		1,378
Recorded Investment With Allowance		0
Total Recorded Investment		1,378
Related Allowance		0
Average Investment in Impaired Loans	1,857
Interest Income Recognized	13
Real Estate
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		34,759
Recorded Investment With No Allowance		24,318
Recorded Investment With Allowance		6,775
Total Recorded Investment		31,093
Related Allowance		740
Average Investment in Impaired Loans	24,615
Interest Income Recognized	176
Real Estate | Construction and development
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		4,648
Recorded Investment With No Allowance		4,466
Recorded Investment With Allowance		72
Total Recorded Investment		4,538
Related Allowance		4
Average Investment in Impaired Loans	1,920
Interest Income Recognized	14
Real Estate | Single family residential
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		19,466
Recorded Investment With No Allowance		15,139
Recorded Investment With Allowance		2,963
Total Recorded Investment		18,102
Related Allowance		42
Average Investment in Impaired Loans	13,703
Interest Income Recognized	98
Real Estate | Other commercial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		10,645
Recorded Investment With No Allowance		4,713
Recorded Investment With Allowance		3,740
Total Recorded Investment		8,453
Related Allowance		694
Average Investment in Impaired Loans	8,992
Interest Income Recognized	64
Commercial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		53,961
Recorded Investment With No Allowance		6,965
Recorded Investment With Allowance		29,114
Total Recorded Investment		36,079
Related Allowance		5,007
Average Investment in Impaired Loans	21,886
Interest Income Recognized	156
Commercial | Commercial
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		53,436
Recorded Investment With No Allowance		6,582
Recorded Investment With Allowance		28,998
Total Recorded Investment		35,580
Related Allowance		5,007
Average Investment in Impaired Loans	20,739
Interest Income Recognized	148
Commercial | Agricultural
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance		525
Recorded Investment With No Allowance		383
Recorded Investment With Allowance		116
Total Recorded Investment		499
Related Allowance		$ 0
Average Investment in Impaired Loans	1,147
Interest Income Recognized	$ 8