Loans and Allowance for Loan Losses - Financing Receivable Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Loans Receivable
Loan Portfolio Internal Grading System Classification	$ 5,225,529	$ 5,052,046
Commercial construction
Loan Portfolio Internal Grading System Classification	1,212,837	1,322,861
Commercial Real Estate
Loan Portfolio Internal Grading System Classification	1,553,677	1,494,172
Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	14,003	13,189
Consumer auto
Loan Portfolio Internal Grading System Classification	86,173	151,854
Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	114,689	118,988
Land development
Loan Portfolio Internal Grading System Classification	54,010	40,431
One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	42,793	33,963
Subdivision construction
Loan Portfolio Internal Grading System Classification	30,894	16,088
Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	470,436	387,016
Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	114,569	120,343
Other residential
Loan Portfolio Internal Grading System Classification	1,021,145	866,006
Commercial business
Loan Portfolio Internal Grading System Classification	370,898	313,209
Consumer other
Loan Portfolio Internal Grading System Classification	40,762	46,720
Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	98,643	127,206
Satisfactory | Loans Receivable
Loan Portfolio Internal Grading System Classification	5,153,396	5,005,765
Satisfactory | Commercial construction
Loan Portfolio Internal Grading System Classification	1,212,837	1,322,861
Satisfactory | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	1,498,031	1,458,400
Satisfactory | Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	14,003	13,189
Satisfactory | Consumer auto
Loan Portfolio Internal Grading System Classification	85,657	150,874
Satisfactory | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	114,049	118,428
Satisfactory | Land development
Loan Portfolio Internal Grading System Classification	54,010	40,431
Satisfactory | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	41,428	33,963
Satisfactory | Subdivision construction
Loan Portfolio Internal Grading System Classification	30,874	16,061
Satisfactory | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	467,855	385,001
Satisfactory | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	114,176	119,743
Satisfactory | Other residential
Loan Portfolio Internal Grading System Classification	1,017,648	866,006
Satisfactory | Commercial business
Loan Portfolio Internal Grading System Classification	363,681	307,322
Satisfactory | Consumer other
Loan Portfolio Internal Grading System Classification	40,514	46,294
Satisfactory | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	98,633	127,192
Watch | Loans Receivable
Loan Portfolio Internal Grading System Classification	64,758	37,368
Watch | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	52,208	32,063
Watch | Consumer auto
Loan Portfolio Internal Grading System Classification	5	47
Watch | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	39	43
Watch | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	1,365
Watch | Subdivision construction
Loan Portfolio Internal Grading System Classification		27
Watch | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	216	26
Watch | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	324	419
Watch | Other residential
Loan Portfolio Internal Grading System Classification	3,497
Watch | Commercial business
Loan Portfolio Internal Grading System Classification	7,102	4,651
Watch | Consumer other
Loan Portfolio Internal Grading System Classification	2	92
Substandard | Loans Receivable
Loan Portfolio Internal Grading System Classification	7,375	8,913
Substandard | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	3,438	3,709
Substandard | Consumer auto
Loan Portfolio Internal Grading System Classification	511	933
Substandard | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	601	517
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	1,989
Substandard | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	69	181
Substandard | Commercial business
Loan Portfolio Internal Grading System Classification	115	1,236
Substandard | Consumer other
Loan Portfolio Internal Grading System Classification	246	334
Substandard | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	$ 10	$ 14