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, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total	$ 14,788,732	$ 14,751,232
Total Loans	14,788,732	14,751,232
Non- accrual	88,083	142,525
90 Days or More Past Due, Still Accruing Interest	1,293	4,395
Current
Financing Receivable, Past Due [Line Items]
Total	14,687,682	14,591,038
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	40,955	47,721
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total	60,095	112,473
Total Past Due
Financing Receivable, Past Due [Line Items]
Total	101,050	160,194
Commercial, industrial, agricultural
Financing Receivable, Past Due [Line Items]
Total	5,054,617	4,942,292
Commercial, industrial, agricultural | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	4,705,458	4,578,254
Total Loans	4,705,458	4,578,254
Non- accrual	14,616	42,965
90 Days or More Past Due, Still Accruing Interest	722	591
Commercial, industrial, agricultural | Agricultural
Financing Receivable, Past Due [Line Items]
Total	349,159	364,038
Total Loans	349,159	364,038
Non- accrual	6,682	10,719
90 Days or More Past Due, Still Accruing Interest	0	0
Commercial, industrial, agricultural | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	4,687,711	4,530,546
Commercial, industrial, agricultural | Current | Agricultural
Financing Receivable, Past Due [Line Items]
Total	344,374	359,373
Commercial, industrial, agricultural | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	6,475	9,254
Commercial, industrial, agricultural | 30-89 Days Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total	1,388	705
Commercial, industrial, agricultural | 90 Days or More Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	11,272	38,454
Commercial, industrial, agricultural | 90 Days or More Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total	3,397	3,960
Commercial, industrial, agricultural | Total Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total	17,747	47,708
Commercial, industrial, agricultural | Total Past Due | Agricultural
Financing Receivable, Past Due [Line Items]
Total	4,785	4,665
Commercial real estate
Financing Receivable, Past Due [Line Items]
Total	4,852,692	4,829,168
Total Loans	4,852,692	4,829,168
Non- accrual	43,993	67,516
90 Days or More Past Due, Still Accruing Interest	32	1,756
Commercial real estate | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total	1,765,592	1,861,768
Total Loans	1,765,592	1,861,768
Non- accrual	20,632	34,224
90 Days or More Past Due, Still Accruing Interest	0	257
Commercial real estate | Multi- family
Financing Receivable, Past Due [Line Items]
Total	1,082,941	872,813
Total Loans	1,082,941	872,813
Non- accrual	3,450	2,488
90 Days or More Past Due, Still Accruing Interest	0	0
Commercial real estate | Construction
Financing Receivable, Past Due [Line Items]
Total	595,204	612,611
Total Loans	595,204	612,611
Non- accrual	1,851	4,980
90 Days or More Past Due, Still Accruing Interest	0	1,065
Commercial real estate | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total	1,408,955	1,481,976
Total Loans	1,408,955	1,481,976
Non- accrual	18,060	25,824
90 Days or More Past Due, Still Accruing Interest	32	434
Commercial real estate | Current
Financing Receivable, Past Due [Line Items]
Total	4,796,517	4,750,898
Commercial real estate | Current | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total	1,738,178	1,827,891
Commercial real estate | Current | Multi- family
Financing Receivable, Past Due [Line Items]
Total	1,077,754	867,815
Commercial real estate | Current | Construction
Financing Receivable, Past Due [Line Items]
Total	592,433	606,934
Commercial real estate | Current | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total	1,388,152	1,448,258
Commercial real estate | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	24,670	22,640
Commercial real estate | 30-89 Days Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total	15,351	3,961
Commercial real estate | 30-89 Days Past Due | Multi- family
Financing Receivable, Past Due [Line Items]
Total	2,085	2,510
Commercial real estate | 30-89 Days Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total	920	1,154
Commercial real estate | 30-89 Days Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total	6,314	15,015
Commercial real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total	31,505	55,630
Commercial real estate | 90 Days or More Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total	12,063	29,916
Commercial real estate | 90 Days or More Past Due | Multi- family
Financing Receivable, Past Due [Line Items]
Total	3,102	2,488
Commercial real estate | 90 Days or More Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total	1,851	4,523
Commercial real estate | 90 Days or More Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total	14,489	18,703
Commercial real estate | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	56,175	78,270
Commercial real estate | Total Past Due | Office, retail, and industrial
Financing Receivable, Past Due [Line Items]
Total	27,414	33,877
Commercial real estate | Total Past Due | Multi- family
Financing Receivable, Past Due [Line Items]
Total	5,187	4,998
Commercial real estate | Total Past Due | Construction
Financing Receivable, Past Due [Line Items]
Total	2,771	5,677
Commercial real estate | Total Past Due | Other commercial real estate
Financing Receivable, Past Due [Line Items]
Total	20,803	33,718
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans
Financing Receivable, Past Due [Line Items]
Total	9,907,309	9,771,460
Total Loans	9,907,309	9,771,460
Non- accrual	65,291	121,200
90 Days or More Past Due, Still Accruing Interest	754	2,347
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans | Current
Financing Receivable, Past Due [Line Items]
Total	9,828,602	9,640,817
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	32,533	32,599
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total	46,174	98,044
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	78,707	130,643
PPP loans
Financing Receivable, Past Due [Line Items]
Total	384,100	785,563
Total Loans	384,100	785,563
Non- accrual	0	0
90 Days or More Past Due, Still Accruing Interest	0	0
PPP loans | Current
Financing Receivable, Past Due [Line Items]
Total	384,100	785,563
PPP loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
PPP loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
PPP loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Total corporate loans
Financing Receivable, Past Due [Line Items]
Total	10,291,409	10,557,023
Total Loans	10,291,409	10,557,023
Non- accrual	65,291	121,200
90 Days or More Past Due, Still Accruing Interest	754	2,347
Total corporate loans | Current
Financing Receivable, Past Due [Line Items]
Total	10,212,702	10,426,380
Total corporate loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	32,533	32,599
Total corporate loans | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total	46,174	98,044
Total corporate loans | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	78,707	130,643
Consumer
Financing Receivable, Past Due [Line Items]
Total	4,497,323	4,194,209
Total Loans	4,497,323	4,194,209
Non- accrual	22,792	21,325
90 Days or More Past Due, Still Accruing Interest	539	2,048
Consumer | Home equity
Financing Receivable, Past Due [Line Items]
Total	591,126	761,725
Total Loans	591,126	761,725
Non- accrual	10,006	10,795
90 Days or More Past Due, Still Accruing Interest	75	956
Consumer | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total	3,332,732	3,022,413
Total Loans	3,332,732	3,022,413
Non- accrual	12,786	10,530
90 Days or More Past Due, Still Accruing Interest	0	115
Consumer | Installment
Financing Receivable, Past Due [Line Items]
Total	573,465	410,071
Total Loans	573,465	410,071
Non- accrual	0	0
90 Days or More Past Due, Still Accruing Interest	464	977
Consumer | Current
Financing Receivable, Past Due [Line Items]
Total	4,474,980	4,164,658
Consumer | Current | Home equity
Financing Receivable, Past Due [Line Items]
Total	585,157	750,263
Consumer | Current | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total	3,319,223	3,009,564
Consumer | Current | Installment
Financing Receivable, Past Due [Line Items]
Total	570,600	404,831
Consumer | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	8,422	15,122
Consumer | 30-89 Days Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total	2,043	5,563
Consumer | 30-89 Days Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total	3,978	5,296
Consumer | 30-89 Days Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total	2,401	4,263
Consumer | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total	13,921	14,429
Consumer | 90 Days or More Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total	3,926	5,899
Consumer | 90 Days or More Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total	9,531	7,553
Consumer | 90 Days or More Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total	464	977
Consumer | Total Past Due
Financing Receivable, Past Due [Line Items]
Total	22,343	29,551
Consumer | Total Past Due | Home equity
Financing Receivable, Past Due [Line Items]
Total	5,969	11,462
Consumer | Total Past Due | 1-4 family mortgages
Financing Receivable, Past Due [Line Items]
Total	13,509	12,849
Consumer | Total Past Due | Installment
Financing Receivable, Past Due [Line Items]
Total	$ 2,865	$ 5,240