Loans and Allowance for Loan Losses, Financing Receivables Past Due (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	$ 22,424,501	$ 19,787,876
Nonaccrual loans	73,836	61,605
Financing Receivable, Nonaccrual, No Allowance	36,537
Currently performing impaired loans	51,700	35,800
Financing Receivable, Past Due	65,045	62,338
Reinsurance Recoverable, Not Past Due	22,359,456	19,725,538
Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	31,881	28,745
Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	15,721	12,333
Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	17,443	21,260
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans		7,709,218
Commercial Real Estate Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	2,802,227	2,669,766
Nonaccrual loans	10,231	11,654
Financing Receivable, Nonaccrual, No Allowance	5,985
Financing Receivable, Past Due	5,466	6,958
Reinsurance Recoverable, Not Past Due	2,796,761	2,662,808
Commercial Real Estate Owner Occupied | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	934	2,307
Commercial Real Estate Owner Occupied | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	2,672	2,932
Commercial Real Estate Owner Occupied | Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	1,860	1,719
Commercial real estate non owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	5,203,384	5,039,452
Nonaccrual loans	5,219	7,173
Financing Receivable, Nonaccrual, No Allowance	1,522
Financing Receivable, Past Due	10,807	10,613
Reinsurance Recoverable, Not Past Due	5,192,577	5,028,839
Commercial real estate non owner occupied | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	726	3,156
Commercial real estate non owner occupied | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	6,220	3,641
Commercial real estate non owner occupied | Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	3,861	3,816
Consumer Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	3,099,172	3,068,625
Financing Receivable, Past Due	15,461	21,107
Reinsurance Recoverable, Not Past Due	3,083,711	3,047,518
Consumer Real Estate | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	8,859	11,646
Consumer Real Estate | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	328	2,157
Consumer Real Estate | Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	6,274	7,304
Construction and Land Development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	2,901,746	2,430,483
Nonaccrual loans	1,953	2,278
Financing Receivable, Nonaccrual, No Allowance	0
Financing Receivable, Past Due	1,432	3,590
Reinsurance Recoverable, Not Past Due	2,900,314	2,426,893
Construction and Land Development | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	278	1,392
Construction and Land Development | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	418	711
Construction and Land Development | Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	736	1,487
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	8,038,457	6,290,296
Financing Receivable, Past Due	30,487	17,316
Reinsurance Recoverable, Not Past Due	8,007,970	6,272,980
Commercial and Industrial | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	20,278	8,474
Commercial and Industrial | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	5,801	2,478
Commercial and Industrial | Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	4,408	6,364
Consumer and Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	379,515	289,254
Nonaccrual loans	4	148
Financing Receivable, Nonaccrual, No Allowance	0
Financing Receivable, Past Due	1,392	2,754
Reinsurance Recoverable, Not Past Due	378,123	286,500
Consumer and Other | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	806	1,770
Consumer and Other | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	282	414
Consumer and Other | Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Past Due	$ 304	$ 570