Loans and Allowance for Credit Losses - Financing Receivable Credit Quality Indicators (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Loans Receivable
Loan Portfolio Internal Grading System Classification	$ 4,361,807
Commercial construction
Loan Portfolio Internal Grading System Classification	484,372
Commercial Real Estate
Loan Portfolio Internal Grading System Classification	1,541,242
Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	14,003
Consumer auto
Loan Portfolio Internal Grading System Classification	86,173
Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	114,689
Land development
Loan Portfolio Internal Grading System Classification	54,010
One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	20,718
Subdivision construction
Loan Portfolio Internal Grading System Classification	4,917
Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	470,310
Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	114,498
Other residential
Loan Portfolio Internal Grading System Classification	999,447
Commercial business
Loan Portfolio Internal Grading System Classification	318,023
Consumer
Loan Portfolio Internal Grading System Classification	40,762
Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	98,643
Satisfactory | Loans Receivable
Loan Portfolio Internal Grading System Classification	4,289,674
Satisfactory | Commercial construction
Loan Portfolio Internal Grading System Classification	484,372
Satisfactory | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	1,485,596
Satisfactory | Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	14,003
Satisfactory | Consumer auto
Loan Portfolio Internal Grading System Classification	85,657
Satisfactory | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	114,049
Satisfactory | Land development
Loan Portfolio Internal Grading System Classification	54,010
Satisfactory | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	19,353
Satisfactory | Subdivision construction
Loan Portfolio Internal Grading System Classification	4,897
Satisfactory | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	467,729
Satisfactory | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	114,105
Satisfactory | Other residential
Loan Portfolio Internal Grading System Classification	995,950
Satisfactory | Commercial business
Loan Portfolio Internal Grading System Classification	310,806
Satisfactory | Consumer
Loan Portfolio Internal Grading System Classification	40,514
Satisfactory | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	98,633
Watch | Loans Receivable
Loan Portfolio Internal Grading System Classification	64,758
Watch | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	52,208
Watch | Consumer auto
Loan Portfolio Internal Grading System Classification	5
Watch | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	39
Watch | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	1,365
Watch | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	216
Watch | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	324
Watch | Other residential
Loan Portfolio Internal Grading System Classification	3,497
Watch | Commercial business
Loan Portfolio Internal Grading System Classification	7,102
Watch | Consumer
Loan Portfolio Internal Grading System Classification	2
Substandard | Loans Receivable
Loan Portfolio Internal Grading System Classification	7,375
Substandard | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	3,438
Substandard | Consumer auto
Loan Portfolio Internal Grading System Classification	511
Substandard | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	601
Substandard | Subdivision construction
Loan Portfolio Internal Grading System Classification	20
Substandard | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	2,365
Substandard | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	69
Substandard | Commercial business
Loan Portfolio Internal Grading System Classification	115
Substandard | Consumer
Loan Portfolio Internal Grading System Classification	246
Substandard | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	$ 10