Fair Value Accounting (Financial Instruments Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	$ 6,937,240	$ 6,778,670
Mortgage loans held for sale	119,841	115,173
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	335,737	371,592
State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	1,005	2,075
Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	145,975	327,400
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	19,918	19,855
Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	55,422	56,816
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	5,549,825	5,180,815
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	628,880	636,851
Corporate debt securities and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	125,622	146,725
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	19,918	19,855
Private equity investments	11,877	15,502
GGL/SBA loans servicing asset	0	0
Derivative assets	0	0
Trading liability for short positions		1,560
Earnout liability	0	0
Derivative liabilities	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	4,857	7,212
Investment securities available for sale	6,915,760	6,756,710
Private equity investments	0	0
GGL/SBA loans servicing asset	0	0
Derivative assets	466,401	140,016
Trading liability for short positions		0
Earnout liability	0	0
Derivative liabilities	184,021
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	1,562	2,105
Private equity investments	3,255	3,887
GGL/SBA loans servicing asset	3,149	3,040
Derivative assets	0	0
Trading liability for short positions		0
Earnout liability	11,016	11,016
Derivative liabilities	2,050
Fair Value, Measurements, Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	4,857	7,212
Investment securities available for sale	6,937,240	6,778,670
Mortgage loans held for sale	119,841	115,173
Private equity investments	15,132	19,389
GGL/SBA loans servicing asset	3,149	3,040
Derivative assets	466,401	140,016
Trading liability for short positions		1,560
Earnout liability	11,016	11,016
Derivative liabilities	186,071	37,071
Fair Value, Measurements, Recurring Basis | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	637	2,486
Investment securities available for sale	335,737	371,592
Fair Value, Measurements, Recurring Basis | Other mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	1,582	1,284
Fair Value, Measurements, Recurring Basis | State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	680	65
Investment securities available for sale	1,005	2,075
Fair Value, Measurements, Recurring Basis | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	1,913	3,227
Investment securities available for sale	145,975	327,400
Fair Value, Measurements, Recurring Basis | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	45	150
Fair Value, Measurements, Recurring Basis | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	19,918	19,855
Fair Value, Measurements, Recurring Basis | U.S. Government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	74,856	36,541
Fair Value, Measurements, Recurring Basis | Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	55,422	56,816
Fair Value, Measurements, Recurring Basis | Mortgage-backed securities issued by U.S. Government sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	5,549,825	5,180,815
Fair Value, Measurements, Recurring Basis | Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	628,880	636,851
Fair Value, Measurements, Recurring Basis | Corporate debt securities and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	125,622	146,725
Fair Value, Measurements, Recurring Basis | Mutual funds and mutual funds held in rabbi trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mutual funds and mutual funds held in rabbi trusts	31,241	32,348
Fair Value, Measurements, Recurring Basis | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	19,918	19,855
Mortgage loans held for sale	0	0
Private equity investments	11,877	15,502
GGL/SBA loans servicing asset	0	0
Trading liability for short positions		1,560
Earnout liability	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Other mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	19,918	19,855
Fair Value, Measurements, Recurring Basis | Level 1 | U.S. Government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Mortgage-backed securities issued by U.S. Government sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Corporate debt securities and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Mutual funds and mutual funds held in rabbi trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mutual funds and mutual funds held in rabbi trusts	31,241	32,348
Fair Value, Measurements, Recurring Basis | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	4,857	7,212
Investment securities available for sale	6,915,760	6,756,710
Mortgage loans held for sale	119,841	115,173
Private equity investments	0	0
GGL/SBA loans servicing asset	0
Trading liability for short positions		0
Earnout liability	0	0
Derivative liabilities	184,021	34,732
Fair Value, Measurements, Recurring Basis | Level 2 | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	637	2,486
Investment securities available for sale	335,737	371,592
Fair Value, Measurements, Recurring Basis | Level 2 | Other mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	1,582	1,284
Fair Value, Measurements, Recurring Basis | Level 2 | State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	680	65
Investment securities available for sale	1,005	2,075
Fair Value, Measurements, Recurring Basis | Level 2 | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	1,913	3,227
Investment securities available for sale	145,975	327,400
Fair Value, Measurements, Recurring Basis | Level 2 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	45	150
Fair Value, Measurements, Recurring Basis | Level 2 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 2 | U.S. Government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	74,856	36,541
Fair Value, Measurements, Recurring Basis | Level 2 | Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	55,422	56,816
Fair Value, Measurements, Recurring Basis | Level 2 | Mortgage-backed securities issued by U.S. Government sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	5,549,825	5,180,815
Fair Value, Measurements, Recurring Basis | Level 2 | Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	628,880	636,851
Fair Value, Measurements, Recurring Basis | Level 2 | Corporate debt securities and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	124,060	144,620
Fair Value, Measurements, Recurring Basis | Level 2 | Mutual funds and mutual funds held in rabbi trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mutual funds and mutual funds held in rabbi trusts	0	0
Fair Value, Measurements, Recurring Basis | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	1,562	2,105
Mortgage loans held for sale	0	0
Private equity investments	3,255	3,887
GGL/SBA loans servicing asset	3,149	3,040
Trading liability for short positions		0
Earnout liability	11,016	11,016
Derivative liabilities	2,050	2,339
Fair Value, Measurements, Recurring Basis | Level 3 | Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Other mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | U.S. Government agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Mortgage-backed securities issued by U.S. Government sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	0	0
Fair Value, Measurements, Recurring Basis | Level 3 | Corporate debt securities and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	1,562	2,105
Fair Value, Measurements, Recurring Basis | Level 3 | Mutual funds and mutual funds held in rabbi trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mutual funds and mutual funds held in rabbi trusts	$ 0	$ 0