Loans - Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 14,788,732	$ 14,751,232
Loans	14,788,732	14,751,232
Deferred loan fees included in total loans	8,688	9,696
Overdrawn demand deposits included in total loans	8,562	8,444
Interest receivable on loan portfolio	51,600	56,700
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	14,687,682	14,591,038
Commercial, industrial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5,054,617	4,942,292
Commercial, industrial, agricultural | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,705,458	4,578,254
Loans	4,705,458	4,578,254
Commercial, industrial, agricultural | Commercial and industrial | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,687,711	4,530,546
Commercial, industrial, agricultural | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	349,159	364,038
Loans	349,159	364,038
Commercial, industrial, agricultural | Agricultural | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	344,374	359,373
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,852,692	4,829,168
Loans	4,852,692	4,829,168
Commercial real estate | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,796,517	4,750,898
Commercial real estate | Office, retail, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,765,592	1,861,768
Loans	1,765,592	1,861,768
Commercial real estate | Office, retail, and industrial | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,738,178	1,827,891
Commercial real estate | Multi- family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,082,941	872,813
Loans	1,082,941	872,813
Commercial real estate | Multi- family | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,077,754	867,815
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	595,204	612,611
Loans	595,204	612,611
Commercial real estate | Construction | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	592,433	606,934
Commercial real estate | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,408,955	1,481,976
Loans	1,408,955	1,481,976
Commercial real estate | Other commercial real estate | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,388,152	1,448,258
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,907,309	9,771,460
Loans	9,907,309	9,771,460
Total corporate loans, excluding Paycheck Protection Program ("PPP") loans | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,828,602	9,640,817
PPP loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	384,100	785,563
Loans	384,100	785,563
PPP loans | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	384,100	785,563
Total corporate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	10,291,409	10,557,023
Loans	10,291,409	10,557,023
Total corporate loans | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	10,212,702	10,426,380
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,497,323	4,194,209
Loans	4,497,323	4,194,209
Consumer | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,474,980	4,164,658
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	591,126	761,725
Loans	591,126	761,725
Consumer | Home equity | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	585,157	750,263
Consumer | 1-4 family mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	3,332,732	3,022,413
Loans	3,332,732	3,022,413
Consumer | 1-4 family mortgages | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	3,319,223	3,009,564
Consumer | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	573,465	410,071
Loans	573,465	410,071
Consumer | Installment | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 570,600	$ 404,831