Past Due Loans, Allowance For Credit Losses, Non-Accrual Loans, and TDRS - Aging Analysis of Past Due Loans and Non-Performing Loans by Class (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 14,507,621	$ 12,754,845
Total Past Due	145,567	85,485
Total Loans	14,653,188	12,840,330
Non-accrual	143,572	82,269
90 Days or More Past Due, Still Accruing Interest	3,781	5,001
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	29,095	35,192
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	116,472	50,293
Commercial industrial and agricultural
Financing Receivable, Past Due [Line Items]
Total Loans	5,013,037	4,887,141
Commercial industrial and agricultural | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Current	4,583,661	4,455,381
Total Past Due	51,910	26,144
Total Loans	4,635,571	4,481,525
Non-accrual	49,866	29,995
90 Days or More Past Due, Still Accruing Interest	1,003	2,207
Commercial industrial and agricultural | Agricultural
Financing Receivable, Past Due [Line Items]
Current	370,387	398,676
Total Past Due	7,079	6,940
Total Loans	377,466	405,616
Non-accrual	13,293	5,954
90 Days or More Past Due, Still Accruing Interest	0	358
Commercial industrial and agricultural | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	4,644	11,468
Commercial industrial and agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due	428	850
Commercial industrial and agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	47,266	14,676
Commercial industrial and agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due	6,651	6,090
Commercial real estate
Financing Receivable, Past Due [Line Items]
Current	4,840,374	4,649,826
Total Past Due	62,926	32,246
Total Loans	4,903,300	4,682,072
Non-accrual	61,795	33,435
90 Days or More Past Due, Still Accruing Interest	1,454	1,075
Commercial real estate | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Current	1,914,480	1,830,321
Total Past Due	35,926	18,397
Total Loans	1,950,406	1,848,718
Non-accrual	35,241	25,857
90 Days or More Past Due, Still Accruing Interest	502	546
Commercial real estate | Multi-family
Financing Receivable, Past Due [Line Items]
Current	865,499	853,762
Total Past Due	2,794	2,791
Total Loans	868,293	856,553
Non-accrual	2,433	2,697
90 Days or More Past Due, Still Accruing Interest	73	0
Commercial real estate | Construction
Financing Receivable, Past Due [Line Items]
Current	624,789	588,065
Total Past Due	6,818	5,028
Total Loans	631,607	593,093
Non-accrual	6,446	152
90 Days or More Past Due, Still Accruing Interest	89	0
Commercial real estate | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Current	1,435,606	1,377,678
Total Past Due	17,388	6,030
Total Loans	1,452,994	1,383,708
Non-accrual	17,675	4,729
90 Days or More Past Due, Still Accruing Interest	790	529
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	12,485	11,263
Commercial real estate | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	2,428	2,943
Commercial real estate | 30-89 Days Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due	395	211
Commercial real estate | 30-89 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due	3,260	4,876
Commercial real estate | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	6,402	3,233
Commercial real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	50,441	20,983
Commercial real estate | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	33,498	15,454
Commercial real estate | 90 Days or More Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due	2,399	2,580
Commercial real estate | 90 Days or More Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due	3,558	152
Commercial real estate | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	10,986	2,797
Total corporate loans, excluding PPP loans
Financing Receivable, Past Due [Line Items]
Current	9,794,422
Total Past Due	121,915
Total Loans	9,916,337	9,569,213
Non-accrual	124,954
90 Days or More Past Due, Still Accruing Interest	2,457
Total corporate loans, excluding PPP loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	17,557
Total corporate loans, excluding PPP loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	104,358
PPP loans
Financing Receivable, Past Due [Line Items]
Total Past Due	0
Total Loans	1,196,538	0
Non-accrual	0
90 Days or More Past Due, Still Accruing Interest	0
PPP loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0
PPP loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0
Total corporate loans
Financing Receivable, Past Due [Line Items]
Current	10,990,960	9,503,883
Total Past Due	121,915	65,330
Total Loans	11,112,875	9,569,213
Non-accrual	124,954	69,384
90 Days or More Past Due, Still Accruing Interest	2,457	3,640
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	17,557	23,581
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	104,358	41,749
Consumer loans
Financing Receivable, Past Due [Line Items]
Current	3,516,661	3,250,962
Total Past Due	23,652	20,155
Total Loans	3,540,313	3,271,117
Non-accrual	18,618	12,885
90 Days or More Past Due, Still Accruing Interest	1,324	1,361
Consumer loans | Home equity
Financing Receivable, Past Due [Line Items]
Current	817,184	841,908
Total Past Due	10,562	9,546
Total Loans	827,746	851,454
Non-accrual	9,548	8,443
90 Days or More Past Due, Still Accruing Interest	19	146
Consumer loans | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Current	2,276,561	1,917,648
Total Past Due	10,994	9,430
Total Loans	2,287,555	1,927,078
Non-accrual	9,070	4,442
90 Days or More Past Due, Still Accruing Interest	445	1,203
Consumer loans | Installment
Financing Receivable, Past Due [Line Items]
Current	422,916	491,406
Total Past Due	2,096	1,179
Total Loans	425,012	492,585
Non-accrual	0	0
90 Days or More Past Due, Still Accruing Interest	860	12
Consumer loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	11,538	11,611
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due	6,014	4,992
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due	4,288	5,452
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due	1,236	1,167
Consumer loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	12,114	8,544
Consumer loans | 90 Days or More Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due	4,548	4,554
Consumer loans | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due	6,706	3,978
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 860	$ 12