Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Noninterest income:
Fixed income	$ 51,000	$ 102,000	$ 124,000	$ 228,000
Deposit transactions and cash management	42,000	44,000	86,000	86,000
Mortgage banking and title income	34,000	38,000	56,000	91,000
Brokerage, management fees and commissions	24,000	21,000	48,000	41,000
Card and digital banking fees	23,000	21,000	43,000	38,000
Other service charges and fees	15,000	11,000	28,000	21,000
Trust services and investment management	12,000	14,000	25,000	26,000
Securities gains (losses), net		11,000	6,000	11,000
Deferred compensation income	(17,000)	7,000	(21,000)	9,000
Other income	17,000	16,000	35,000	32,000
Total noninterest income	201,000	285,000	430,000	583,000
Underwriting, portfolio advisory, and other noninterest income
Noninterest income:
Revenue from contract with customer	10,000	14,000	21,000	24,000
Regional Banking
Noninterest income:
Fixed income	0	0	0	1,000
Deposit transactions and cash management	38,000	39,000	77,000	77,000
Mortgage banking and title income	0	0	0	0
Brokerage, management fees and commissions	24,000	21,000	48,000	41,000
Card and digital banking fees	21,000	18,000	38,000	32,000
Other service charges and fees	9,000	6,000	16,000	12,000
Trust services and investment management	12,000	14,000	25,000	26,000
Securities gains (losses), net		0	0	0
Deferred compensation income	0	0	0	0
Other income	10,000	11,000	23,000	21,000
Total noninterest income	114,000	109,000	227,000	210,000
Specialty Banking
Noninterest income:
Fixed income	51,000	102,000	124,000	227,000
Deposit transactions and cash management	2,000	3,000	5,000	6,000
Mortgage banking and title income	34,000	38,000	56,000	90,000
Brokerage, management fees and commissions	0	0	0	0
Card and digital banking fees	0	1,000	1,000	2,000
Other service charges and fees	6,000	4,000	11,000	7,000
Trust services and investment management	0	0	0	0
Securities gains (losses), net		0	0	0
Deferred compensation income	0	0	0	0
Other income	3,000	1,000	4,000	3,000
Total noninterest income	96,000	149,000	201,000	335,000
Corporate
Noninterest income:
Fixed income	0	0	0	0
Deposit transactions and cash management	2,000	2,000	4,000	3,000
Mortgage banking and title income	0	0	0	1,000
Brokerage, management fees and commissions	0	0	0	0
Card and digital banking fees	2,000	2,000	4,000	4,000
Other service charges and fees	0	1,000	1,000	2,000
Trust services and investment management	0	0	0	0
Securities gains (losses), net		11,000	6,000	11,000
Deferred compensation income	(17,000)	7,000	(21,000)	9,000
Other income	4,000	4,000	8,000	8,000
Total noninterest income	$ (9,000)	$ 27,000	$ 2,000	$ 38,000