Loans - Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 14,653,188	$ 12,840,330
Interest receivable on securities	9,608	7,972
Overdrawn demand deposits included in total loans	7,906	10,675
Interest receivable on loan portfolio	56,300	48,400
Commercial industrial and agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5,013,037	4,887,141
Commercial industrial and agricultural | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,635,571	4,481,525
Commercial industrial and agricultural | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	377,466	405,616
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,903,300	4,682,072
Commercial real estate | Office, retail, and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,950,406	1,848,718
Commercial real estate | Multi-family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	868,293	856,553
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	631,607	593,093
Commercial real estate | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,452,994	1,383,708
Total corporate loans, excluding PPP loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	9,916,337	9,569,213
PPP loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,196,538	0
Total corporate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	11,112,875	9,569,213
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	3,540,313	3,271,117
Consumer loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	827,746	851,454
Consumer loans | 1-4 family mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	2,287,555	1,927,078
Consumer loans | Installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 425,012	$ 492,585