Loans - Aging analysis of past due loans (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Loans and Allowance for Loan Losses
Past due	$ 31,718
Current	25,095,203
Non-Accruing	110,894
Total loans - ASU 2016-13	25,237,815
Greater than 90 Days Accruing	1,542
30 days past due
Loans and Allowance for Loan Losses
Past due	21,605
60 days past due
Loans and Allowance for Loan Losses
Past due	8,571
90 days past due
Loans and Allowance for Loan Losses
Past due	1,542
Construction and land development
Loans and Allowance for Loan Losses
Past due	2,273
Current	1,836,193
Non-Accruing	1,645
Total loans - ASU 2016-13	1,840,111
Construction and land development | 30 days past due
Loans and Allowance for Loan Losses
Past due	2,028
Construction and land development | 60 days past due
Loans and Allowance for Loan Losses
Past due	245
Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Past due	6,679
Current	4,271,410
Non-Accruing	33,097
Total loans - ASU 2016-13	4,311,186
Consumer Owner Occupied Loans | 30 days past due
Loans and Allowance for Loan Losses
Past due	2,184
Consumer Owner Occupied Loans | 60 days past due
Loans and Allowance for Loan Losses
Past due	4,494
Consumer Owner Occupied Loans | 90 days past due
Loans and Allowance for Loan Losses
Past due	1
Other income producing property
Loans and Allowance for Loan Losses
Past due	1,261
Current	620,112
Non-Accruing	8,124
Total loans - ASU 2016-13	629,497
Other income producing property | 30 days past due
Loans and Allowance for Loan Losses
Past due	1,261
Other loans
Loans and Allowance for Loan Losses
Current	7,540
Total loans - ASU 2016-13	7,540
Commercial loans
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	17,982,997
Commercial loans | Construction and land development
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	1,157,423
Commercial loans | Commercial non-owner occupied
Loans and Allowance for Loan Losses
Past due	625
Current	5,928,700
Non-Accruing	7,047
Total loans - ASU 2016-13	5,936,372
Commercial loans | Commercial non-owner occupied | 30 days past due
Loans and Allowance for Loan Losses
Past due	604
Commercial loans | Commercial non-owner occupied | 60 days past due
Loans and Allowance for Loan Losses
Past due	21
Commercial loans | Commercial owner occupied real estate loan
Loans and Allowance for Loan Losses
Past due	2,535
Current	4,812,672
Non-Accruing	30,813
Total loans - ASU 2016-13	4,846,020
Greater than 90 Days Accruing	526
Commercial loans | Commercial owner occupied real estate loan | 30 days past due
Loans and Allowance for Loan Losses
Past due	1,150
Commercial loans | Commercial owner occupied real estate loan | 60 days past due
Loans and Allowance for Loan Losses
Past due	859
Commercial loans | Commercial owner occupied real estate loan | 90 days past due
Loans and Allowance for Loan Losses
Past due	526
Commercial loans | Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	34,890
Commercial loans | Commercial and industrial
Loans and Allowance for Loan Losses
Past due	12,867
Current	5,393,529
Non-Accruing	12,724
Total loans - ASU 2016-13	5,419,120
Greater than 90 Days Accruing	632
Commercial loans | Commercial and industrial | 30 days past due
Loans and Allowance for Loan Losses
Past due	10,728
Commercial loans | Commercial and industrial | 60 days past due
Loans and Allowance for Loan Losses
Past due	1,507
Commercial loans | Commercial and industrial | 90 days past due
Loans and Allowance for Loan Losses
Past due	632
Commercial loans | Other income producing property
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	581,632
Commercial loans | Other loans
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	7,540
Consumer
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	7,254,818
Consumer | 30 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	8,627
Consumer | 60 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	6,136
Consumer | 90 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	17,611
Consumer | Construction and land development
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	682,688
Consumer | Construction and land development | 30 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	27
Consumer | Construction and land development | 60 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	47
Consumer | Construction and land development | 90 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	107
Consumer | Consumer Owner Occupied Loans
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	4,276,296
Greater than 90 Days Accruing	1
Consumer | Consumer Owner Occupied Loans | 30 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	3,220
Consumer | Consumer Owner Occupied Loans | 60 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	4,495
Consumer | Consumer Owner Occupied Loans | 90 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	9,876
Consumer | Home equity loans
Loans and Allowance for Loan Losses
Past due	2,852
Current	1,333,516
Non-Accruing	11,430
Total loans - ASU 2016-13	1,347,798
Greater than 90 Days Accruing	379
Consumer | Home equity loans | 30 days past due
Loans and Allowance for Loan Losses
Past due	1,997
Total loans - ASU 2016-13	3,517
Consumer | Home equity loans | 60 days past due
Loans and Allowance for Loan Losses
Past due	476
Total loans - ASU 2016-13	655
Consumer | Home equity loans | 90 days past due
Loans and Allowance for Loan Losses
Past due	379
Total loans - ASU 2016-13	5,360
Consumer | Other income producing property
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	47,865
Consumer | Other income producing property | 90 days past due
Loans and Allowance for Loan Losses
Total loans - ASU 2016-13	15
Consumer | Consumer
Loans and Allowance for Loan Losses
Past due	2,626
Current	891,531
Non-Accruing	6,014
Total loans - ASU 2016-13	900,171
Greater than 90 Days Accruing	4
Consumer | Consumer | 30 days past due
Loans and Allowance for Loan Losses
Past due	1,653
Total loans - ASU 2016-13	1,863
Consumer | Consumer | 60 days past due
Loans and Allowance for Loan Losses
Past due	969
Total loans - ASU 2016-13	939
Consumer | Consumer | 90 days past due
Loans and Allowance for Loan Losses
Past due	4
Total loans - ASU 2016-13	$ 2,253