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	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 14,780,524	$ 12,754,845
Total Past Due	153,134	85,485
Total Loans	14,933,658	12,840,330
Non-accrual	139,160	82,269
90 Days or More Past Due, Still Accruing Interest	3,241	5,001
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	41,532	35,192
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	111,602	50,293
Commercial Industrial And Agricultural
Financing Receivable, Past Due [Line Items]
Total Loans	5,170,680	4,887,141
Commercial Industrial And Agricultural | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Current	4,750,932	4,455,381
Total Past Due	38,624	26,144
Total Loans	4,789,556	4,481,525
Non-accrual	28,349	29,995
90 Days or More Past Due, Still Accruing Interest	1,090	2,207
Commercial Industrial And Agricultural | Agricultural
Financing Receivable, Past Due [Line Items]
Current	373,910	398,676
Total Past Due	7,214	6,940
Total Loans	381,124	405,616
Non-accrual	8,494	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	20,550	11,468
Commercial Industrial And Agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due	0	850
Commercial Industrial And Agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	18,074	14,676
Commercial Industrial And Agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due	7,214	6,090
Commercial real estate
Financing Receivable, Past Due [Line Items]
Current	4,970,994	4,649,826
Total Past Due	87,185	32,246
Total Loans	5,058,179	4,682,072
Non-accrual	84,690	33,435
90 Days or More Past Due, Still Accruing Interest	709	1,075
Commercial real estate | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Current	1,982,798	1,830,321
Total Past Due	37,520	18,397
Total Loans	2,020,318	1,848,718
Non-accrual	35,915	25,857
90 Days or More Past Due, Still Accruing Interest	596	546
Commercial real estate | Multi-family
Financing Receivable, Past Due [Line Items]
Current	870,430	853,762
Total Past Due	4,431	2,791
Total Loans	874,861	856,553
Non-accrual	3,121	2,697
90 Days or More Past Due, Still Accruing Interest	0	0
Commercial real estate | Construction
Financing Receivable, Past Due [Line Items]
Current	658,892	588,065
Total Past Due	28,171	5,028
Total Loans	687,063	593,093
Non-accrual	27,282	152
90 Days or More Past Due, Still Accruing Interest	88	0
Commercial real estate | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Current	1,458,874	1,377,678
Total Past Due	17,063	6,030
Total Loans	1,475,937	1,383,708
Non-accrual	18,372	4,729
90 Days or More Past Due, Still Accruing Interest	25	529
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	12,457	11,263
Commercial real estate | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	4,973	2,943
Commercial real estate | 30-89 Days Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due	1,538	211
Commercial real estate | 30-89 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due	801	4,876
Commercial real estate | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	5,145	3,233
Commercial real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	74,728	20,983
Commercial real estate | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total Past Due	32,547	15,454
Commercial real estate | 90 Days or More Past Due | Multi-family
Financing Receivable, Past Due [Line Items]
Total Past Due	2,893	2,580
Commercial real estate | 90 Days or More Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due	27,370	152
Commercial real estate | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	11,918	2,797
Commercial Portfolio Segment, Excluding PPP Loans
Financing Receivable, Past Due [Line Items]
Current	10,095,836
Total Past Due	133,023
Total Loans	10,228,859
Non-accrual	121,533
90 Days or More Past Due, Still Accruing Interest	1,799
Commercial Portfolio Segment, Excluding PPP Loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	33,007
Commercial Portfolio Segment, Excluding PPP Loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	100,016
PPP loans
Financing Receivable, Past Due [Line Items]
Total Past Due	0
Total Loans	1,179,403
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	11,275,239	9,503,883
Total Past Due	133,023	65,330
Total Loans	11,408,262	9,569,213
Non-accrual	121,533	69,384
90 Days or More Past Due, Still Accruing Interest	1,799	3,640
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	33,007	23,581
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	100,016	41,749
Consumer loans
Financing Receivable, Past Due [Line Items]
Current	3,505,285	3,250,962
Total Past Due	20,111	20,155
Total Loans	3,525,396	3,271,117
Non-accrual	17,627	12,885
90 Days or More Past Due, Still Accruing Interest	1,442	1,361
Consumer loans | Home equity
Financing Receivable, Past Due [Line Items]
Current	885,678	841,908
Total Past Due	7,189	9,546
Total Loans	892,867	851,454
Non-accrual	9,129	8,443
90 Days or More Past Due, Still Accruing Interest	187	146
Consumer loans | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Current	2,164,611	1,917,648
Total Past Due	10,711	9,430
Total Loans	2,175,322	1,927,078
Non-accrual	8,498	4,442
90 Days or More Past Due, Still Accruing Interest	0	1,203
Consumer loans | Installment
Financing Receivable, Past Due [Line Items]
Current	454,996	491,406
Total Past Due	2,211	1,179
Total Loans	457,207	492,585
Non-accrual	0	0
90 Days or More Past Due, Still Accruing Interest	1,255	12
Consumer loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	8,525	11,611
Consumer loans | 30-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total Past Due	2,641	4,992
Consumer loans | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total Past Due	4,928	5,452
Consumer loans | 30-89 Days Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due	956	1,167
Consumer loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	11,586	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	5,783	3,978
Consumer loans | 90 Days or More Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 1,255	$ 12