Fair Value Accounting (Financial Instruments Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities		$ 7,212
Investment securities available for sale	$ 7,566,525	6,778,670
Mortgages Held-for-sale, Fair Value Disclosure		115,173
Private equity investments		19,389
GGL/SBA loans servicing asset		3,040
Derivative assets		140,016
Earnout liability		11,016
Derivative liabilities		37,071
Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	1,129,392	56,816
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	354,157	371,592
State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	501	2,075
Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale		327,400
U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	20,254	19,855
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	4,540,386	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	1,345,284	636,851
Corporate debt securities and other debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment securities available for sale	19,937	146,725
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	20,254	19,855
Private equity investments	0	15,502
Mutual funds and mutual funds held in rabbi trusts	35,174	32,348
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	4,371	7,212
Investment securities available for sale	7,544,471	6,756,710
Mortgages Held-for-sale, Fair Value Disclosure	285,899
Private equity investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	0	0
Derivative assets	463,028	140,016
Trading liability for short positions		0
Earnout liability	0	0
Derivative liabilities	178,508	34,732
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0	0
Investment securities available for sale	1,800	2,105
Private equity investments	958	3,887
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	3,100	3,040
Derivative assets	0	0
Trading liability for short positions		0
Earnout liability	15,924	11,016
Derivative liabilities	1,460	2,339
Fair Value, Measurements, Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	4,371
Mortgages Held-for-sale, Fair Value Disclosure	285,899
Private equity investments	958
Mutual funds and mutual funds held in rabbi trusts	35,174	32,348
GGL/SBA loans servicing asset	3,100
Derivative assets	463,028
Trading liability for short positions		1,560
Earnout liability	15,924
Derivative liabilities	179,968
Fair Value, Measurements, Recurring Basis | Mortgage-backed securities issued by U.S. Government agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	18
Investment securities available for sale	1,129,392	56,816
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	604	2,486
Investment securities available for sale	354,157	371,592
Fair Value, Measurements, Recurring Basis | Other mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	673	1,284
Fair Value, Measurements, Recurring Basis | State and municipal securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	579	65
Investment securities available for sale	501	2,075
Fair Value, Measurements, Recurring Basis | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	2,497	3,227
Investment securities available for sale		327,400
Fair Value, Measurements, Recurring Basis | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities		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	20,254	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	156,614	36,541
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	4,540,386	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	1,345,284	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	19,937	146,725
Fair Value, Measurements, Recurring Basis | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Private equity investments	0	15,502
Mutual funds and mutual funds held in rabbi trusts	35,174	32,348
GGL/SBA loans servicing asset	0	0
Derivative assets	0
Trading liability for short positions		1,560
Earnout liability	0	0
Derivative liabilities	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]
Trading securities	0
Investment securities available for sale	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
Fair Value, Measurements, Recurring Basis | Level 1 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities		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	20,254
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 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 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	4,371
Mortgages Held-for-sale, Fair Value Disclosure	285,899	115,173
Private equity investments	0	0
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	0	0
Derivative assets	463,028
Trading liability for short positions		0
Earnout liability	0	0
Derivative liabilities	178,508
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]
Trading securities	18
Investment securities available for sale	1,129,392	56,816
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		2,486
Investment securities available for sale	354,157	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	673	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	579	65
Investment securities available for sale	501	2,075
Fair Value, Measurements, Recurring Basis | Level 2 | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	2,497	3,227
Investment securities available for sale		327,400
Fair Value, Measurements, Recurring Basis | Level 2 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities		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	156,614	36,541
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	4,540,386	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]
Trading securities	604
Investment securities available for sale	1,345,284	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	18,137	144,620
Fair Value, Measurements, Recurring Basis | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities	0
Investment securities available for sale	1,800	2,105
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Private equity investments	958	3,887
Mutual funds and mutual funds held in rabbi trusts	0	0
GGL/SBA loans servicing asset	3,100	3,040
Derivative assets	0
Trading liability for short positions		0
Earnout liability	15,924	11,016
Derivative liabilities	1,460
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]
Trading securities	0
Investment securities available for sale	0	0
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
Fair Value, Measurements, Recurring Basis | Level 3 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading securities		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 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	$ 1,800	$ 2,105