Fair Value Accounting (Carrying and Estimated Fair Values of Financial Instruments Carried on Balance Sheet) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financial assets
Investment securities available for sale	$ 9,442,170	$ 7,962,438
Loans held for sale	750,916	760,123
Financial liabilities
Non-interest-bearing deposits	15,345,629	13,477,854
Total deposits	47,171,962	46,691,571
Federal funds purchased and securities sold under repurchase agreements	194,786	227,922
Long-term debt	1,203,293	1,202,494
Level 1
Financial assets
Total cash, cash equivalents, and restricted cash	3,262,676	4,252,917
Trading securities	0	0
Investment securities available for sale	118,231	20,257
Loans held for sale	0	0
Private equity investments	0	0
Mutual funds and mutual funds held in rabbi trusts	41,710	37,650
Loans, net	0	0
GGL/SBA loans servicing asset	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	194,786	227,922
Trading liability for short positions		0
Long-term debt	0	0
Earnout liability	0	0
Derivative liabilities	0	0
Level 2
Financial assets
Total cash, cash equivalents, and restricted cash	0	0
Trading securities	4,187	10,880
Investment securities available for sale	9,323,939	7,940,160
Loans held for sale	202,216	216,647
Private equity investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
Loans, net	0	0
GGL/SBA loans servicing asset	0	0
Derivative assets	279,454	401,295
Financial liabilities
Non-interest-bearing deposits	15,345,629	13,477,854
Non-time interest-bearing deposits	27,181,793	27,265,521
Time deposits	4,663,354	5,970,146
Total deposits	47,190,776	46,713,521
Federal funds purchased and securities sold under repurchase agreements	0	0
Trading liability for short positions		7,717
Long-term debt	1,261,642	1,266,825
Earnout liability	0	0
Derivative liabilities	113,708	155,119
Level 3
Financial assets
Total cash, cash equivalents, and restricted cash	0	0
Trading securities	0	0
Investment securities available for sale	0	2,021
Loans held for sale	549,416	544,292
Private equity investments	1,026	1,021
Mutual funds and mutual funds held in rabbi trusts	0	0
Loans, net	37,743,546	37,605,881
GGL/SBA loans servicing asset	3,321	3,258
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
Trading liability for short positions		0
Long-term debt	0	0
Earnout liability	6,427	5,677
Derivative liabilities	1,473	2,048
Carrying Value
Financial assets
Total cash, cash equivalents, and restricted cash	3,262,676	4,252,917
Trading securities	4,187	10,880
Investment securities available for sale	9,442,170	7,962,438
Loans held for sale	750,916	760,123
Private equity investments	1,026	1,021
Mutual funds and mutual funds held in rabbi trusts	41,710	37,650
Loans, net	37,719,310	37,647,248
GGL/SBA loans servicing asset	3,321	3,258
Derivative assets	279,454	401,295
Financial liabilities
Non-interest-bearing deposits	15,345,629	13,477,854
Non-time interest-bearing deposits	27,181,793	27,265,521
Time deposits	4,644,540	5,948,196
Total deposits	47,171,962	46,691,571
Federal funds purchased and securities sold under repurchase agreements	194,786	227,922
Trading liability for short positions		7,717
Long-term debt	1,203,293	1,202,494
Earnout liability	6,427	5,677
Derivative liabilities	115,181	157,167
Fair Value
Financial assets
Total cash, cash equivalents, and restricted cash	3,262,676	4,252,917
Trading securities	4,187	10,880
Investment securities available for sale	9,442,170	7,962,438
Loans held for sale	751,632	760,939
Private equity investments	1,026	1,021
Mutual funds and mutual funds held in rabbi trusts	41,710	37,650
Loans, net	37,743,546	37,605,881
GGL/SBA loans servicing asset	3,321	3,258
Derivative assets	279,454	401,295
Financial liabilities
Non-interest-bearing deposits	15,345,629	13,477,854
Non-time interest-bearing deposits	27,181,793	27,265,521
Time deposits	4,663,354	5,970,146
Total deposits	47,190,776	46,713,521
Federal funds purchased and securities sold under repurchase agreements	194,786	227,922
Trading liability for short positions		7,717
Long-term debt	1,261,642	1,266,825
Earnout liability	6,427	5,677
Derivative liabilities	$ 115,181	$ 157,167