Loans - Schedule of Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Loans [Line Items]
Total loans, net of unearned income	$ 47,067,447	$ 42,131,831	$ 41,446,032
Total loans, net of unearned income, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Total loans, net of unearned income	$ 15,247,693	$ 12,832,053	$ 12,725,473
Total loans, net of unearned income, percentage	33.00%	30.00%	31.00%
Commercial real estate
Loans [Line Items]
Total loans, net of unearned income	$ 12,793,417	$ 11,344,164	$ 10,946,180
Total loans, net of unearned income, percentage	27.00%	27.00%	26.00%
Home equity
Loans [Line Items]
Total loans, net of unearned income	$ 427,043	$ 343,976	$ 343,258
Total loans, net of unearned income, percentage	1.00%	1.00%	1.00%
Residential real estate
Loans [Line Items]
Total loans, net of unearned income	$ 3,388,038	$ 2,769,666	$ 2,707,603
Total loans, net of unearned income, percentage	7.00%	7.00%	7.00%
Premium finance receivables | Premium finance receivables—property & casualty
Loans [Line Items]
Total loans, net of unearned income	$ 7,131,681	$ 6,903,529	$ 6,722,747
Total loans, net of unearned income, percentage	15.00%	16.00%	16.00%
Premium finance receivables | Premium finance receivables—life insurance
Loans [Line Items]
Total loans, net of unearned income	$ 7,996,899	$ 7,877,943	$ 7,931,808
Total loans, net of unearned income, percentage	17.00%	19.00%	19.00%
Consumer and other
Loans [Line Items]
Total loans, net of unearned income	$ 82,676	$ 60,500	$ 68,963
Total loans, net of unearned income, percentage	0.00%	0.00%	0.00%