Fair Value Accounting (Carrying and Estimated Fair Values of Financial Instruments Carried on Balance Sheet) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Financial assets
Investment securities available for sale	$ 9,732,618	$ 9,678,103
Loans held for sale	669,447	391,502
Financial liabilities
Non-interest-bearing deposits	14,642,677	15,639,899
Total deposits	49,953,936	48,871,559
Federal funds purchased and securities sold under repurchase agreements	195,695	146,588
Long-term debt	5,146,252	4,109,597
Level 1
Financial assets
Total cash, cash equivalents, and restricted cash	3,365,400	1,977,780
Trading securities	0	0
Investment securities available for sale	480,280	471,813
Loans held for sale	0	0
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	48,428	42,659
Loans, net	0	0
SBA loans servicing asset	0	0
FRB and FHLB stock	0	0
Derivative assets	0	0
Financial liabilities
Non-interest-bearing deposits	0	0
Non-time interest-bearing deposits	0	0
Time deposits	0	0
Total deposits	0	0
Federal funds purchased and securities sold under repurchase agreements	195,695	146,588
Securities sold short	3,152	3,370
Other short-term borrowings	0	0
Long-term debt	0	0
Mutual funds held in rabbi trusts	33,470	27,944
Derivative liabilities	0	0
Level 2
Financial assets
Total cash, cash equivalents, and restricted cash	0	0
Trading securities	25,915	8,295
Investment securities available for sale	9,252,338	9,206,290
Loans held for sale	44,400	51,136
Other investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
Loans, net	0	0
SBA loans servicing asset	0	0
FRB and FHLB stock	322,869	308,321
Derivative assets	88,257	89,815
Financial liabilities
Non-interest-bearing deposits	14,642,677	15,639,899
Non-time interest-bearing deposits	27,173,132	26,936,635
Time deposits	8,154,023	6,260,315
Total deposits	49,969,832	48,836,849
Federal funds purchased and securities sold under repurchase agreements	0	0
Securities sold short	0	0
Other short-term borrowings	250,000	600,014
Long-term debt	5,019,616	4,120,113
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	318,999	339,227
Level 3
Financial assets
Total cash, cash equivalents, and restricted cash	0	0
Trading securities	0	0
Investment securities available for sale	0	0
Loans held for sale	624,642	339,949
Other investments	11,655	11,172
Mutual funds and mutual funds held in rabbi trusts	0	0
Loans, net	41,958,157	42,192,295
SBA loans servicing asset	2,412	2,354
FRB and FHLB stock		0
Derivative assets	0	0
Financial liabilities
Non-interest-bearing deposits	0	0
Non-time interest-bearing deposits	0	0
Time deposits	0	0
Total deposits	0	0
Federal funds purchased and securities sold under repurchase agreements	0	0
Securities sold short	0	0
Other short-term borrowings	0	0
Long-term debt	0	0
Mutual funds held in rabbi trusts	0	0
Derivative liabilities	1,111	3,453
Carrying Value
Financial assets
Total cash, cash equivalents, and restricted cash	3,365,400	1,977,780
Trading securities	25,915	8,295
Investment securities available for sale	9,732,618	9,678,103
Loans held for sale		391,502
Other investments	11,655	11,172
Mutual funds and mutual funds held in rabbi trusts	48,428	42,659
Loans, net	43,587,929	43,272,929
SBA loans servicing asset	2,412	2,354
FRB and FHLB stock	322,869	308,321
Derivative assets	88,257	89,815
Financial liabilities
Non-interest-bearing deposits	14,642,677	15,639,899
Non-time interest-bearing deposits	27,173,132	26,936,635
Time deposits	8,138,127	6,295,025
Total deposits	49,953,936	48,871,559
Federal funds purchased and securities sold under repurchase agreements	195,695	146,588
Securities sold short	3,152	3,370
Other short-term borrowings	250,000	600,014
Long-term debt	5,146,252	4,109,597
Mutual funds held in rabbi trusts	33,470	27,944
Derivative liabilities	320,110	342,680
Fair Value
Financial assets
Total cash, cash equivalents, and restricted cash	3,365,400	1,977,780
Trading securities	25,915	8,295
Investment securities available for sale	9,732,618	9,678,103
Loans held for sale	669,042	391,085
Other investments	11,655	11,172
Mutual funds and mutual funds held in rabbi trusts	48,428	42,659
Loans, net	41,958,157	42,192,295
SBA loans servicing asset	2,412	2,354
FRB and FHLB stock	322,869	308,321
Derivative assets	88,257	89,815
Financial liabilities
Non-interest-bearing deposits	14,642,677	15,639,899
Non-time interest-bearing deposits	27,173,132	26,936,635
Time deposits	8,154,023	6,260,315
Total deposits	49,969,832	48,836,849
Federal funds purchased and securities sold under repurchase agreements	195,695	146,588
Securities sold short	3,152	3,370
Other short-term borrowings	250,000	600,014
Long-term debt	5,019,616	4,120,113
Mutual funds held in rabbi trusts	33,470	27,944
Derivative liabilities	$ 320,110	$ 342,680