Fair Value Accounting (Carrying and Estimated Fair Values of Financial Instruments Carried on Balance Sheet) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financial assets
Investment securities available for sale	$ 6,937,240	$ 6,778,670
Loans, net	37,764,572	36,881,048
Financial liabilities
Non-interest-bearing deposits	9,659,451	9,439,485
Total deposits	39,826,585	38,405,504
Federal funds purchased and securities sold under repurchase agreements	312,776	165,690
Other short-term borrowings	1,175,000	1,753,560
Long-term debt	3,152,339	2,153,897
Mortgage loans held for sale
Financial assets
Loans receivable held-for-sale	119,841	115,173
Level 1
Financial assets
Total cash, cash equivalents, restricted cash, and restricted cash equivalents	1,823,834	1,186,918
Trading securities	0	0
Investment securities available for sale	19,918	19,855
Private equity investments	11,877	15,502
Mutual funds and mutual funds held in rabbi trusts	31,241	32,348
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	312,776	165,690
Trading liability for short positions		1,560
Other short-term borrowings	0	0
Long-term debt	0	0
Earnout liability	0	0
Derivative liabilities	0	0
Level 1 | Mortgage loans held for sale
Financial assets
Loans receivable held-for-sale	0	0
Level 2
Financial assets
Total cash, cash equivalents, restricted cash, and restricted cash equivalents	0	0
Trading securities	4,857	7,212
Investment securities available for sale	6,915,760	6,756,710
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	466,401	140,016
Financial liabilities
Non-interest-bearing deposits	9,659,451	9,439,485
Non-time interest-bearing deposits	21,305,350	19,891,711
Time deposits	8,934,652	9,112,459
Total deposits	39,899,453	38,443,655
Federal funds purchased and securities sold under repurchase agreements	0	0
Trading liability for short positions		0
Other short-term borrowings	1,175,000	1,752,000
Long-term debt	3,122,480	2,185,717
Earnout liability	0	0
Derivative liabilities	184,021
Level 2 | Mortgage loans held for sale
Financial assets
Loans receivable held-for-sale	119,841	115,173
Level 3
Financial assets
Total cash, cash equivalents, restricted cash, and restricted cash equivalents	0	0
Trading securities	0	0
Investment securities available for sale	1,562	2,105
Private equity investments	3,255	3,887
Mutual funds and mutual funds held in rabbi trusts	0	0
Loans, net	38,168,063	36,931,256
GGL/SBA loans servicing asset	3,149	3,040
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
Other short-term borrowings	0	0
Long-term debt	0	0
Earnout liability	11,016	11,016
Derivative liabilities	2,050
Level 3 | Mortgage loans held for sale
Financial assets
Loans receivable held-for-sale	0	0
Carrying Value
Financial assets
Total cash, cash equivalents, restricted cash, and restricted cash equivalents	1,823,834	1,186,918
Trading securities	4,857	7,212
Investment securities available for sale	6,937,240	6,778,670
Private equity investments	15,132	19,389
Mutual funds and mutual funds held in rabbi trusts	31,241	32,348
Loans, net	37,764,572	36,881,048
GGL/SBA loans servicing asset	3,149	3,040
Derivative assets	466,401	140,016
Financial liabilities
Non-interest-bearing deposits	9,659,451	9,439,485
Non-time interest-bearing deposits	21,305,350	19,891,711
Time deposits	8,861,784	9,074,308
Total deposits	39,826,585	38,405,504
Federal funds purchased and securities sold under repurchase agreements	312,776	165,690
Trading liability for short positions		1,560
Other short-term borrowings	1,175,000	1,752,000
Long-term debt	3,152,339	2,153,897
Earnout liability	11,016	11,016
Derivative liabilities	186,071	37,071
Carrying Value | Mortgage loans held for sale
Financial assets
Loans receivable held-for-sale	119,841	115,173
Fair Value
Financial assets
Total cash, cash equivalents, restricted cash, and restricted cash equivalents	1,823,834	1,186,918
Trading securities	4,857	7,212
Investment securities available for sale	6,937,240	6,778,670
Private equity investments	15,132	19,389
Mutual funds and mutual funds held in rabbi trusts	31,241	32,348
Loans, net	38,168,063	36,931,256
GGL/SBA loans servicing asset	3,149	3,040
Derivative assets	466,401	140,016
Financial liabilities
Non-interest-bearing deposits	9,659,451	9,439,485
Non-time interest-bearing deposits	21,305,350	19,891,711
Time deposits	8,934,652	9,112,459
Total deposits	39,899,453	38,443,655
Federal funds purchased and securities sold under repurchase agreements	312,776	165,690
Trading liability for short positions		1,560
Other short-term borrowings	1,175,000	1,752,000
Long-term debt	3,122,480	2,185,717
Earnout liability	11,016	11,016
Derivative liabilities	186,071	37,071
Fair Value | Mortgage loans held for sale
Financial assets
Loans receivable held-for-sale	$ 119,841	$ 115,173