Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Noninterest income:
Deposit transactions and cash management	$ 45,000	$ 42,000	$ 87,000	$ 86,000
Fixed income	30,000	51,000	69,000	124,000
Brokerage, management fees and commissions	22,000	24,000	44,000	48,000
Card and digital banking fees	21,000	23,000	40,000	43,000
Other service charges and fees	14,000	15,000	27,000	28,000
Trust services and investment management	12,000	12,000	24,000	25,000
Mortgage banking and title income	6,000	34,000	11,000	56,000
Deferred compensation income	8,000	(17,000)	11,000	(21,000)
Gain on merger termination	225,000	0	225,000	0
Securities gains (losses), net	0	0	1,000	6,000
Other income	17,000	17,000	32,000	35,000
Total noninterest income	400,000	201,000	571,000	430,000
Underwriting, portfolio advisory, and other noninterest income
Noninterest income:
Revenue from contract with customer	9,000	10,000	19,000	21,000
Regional Banking
Noninterest income:
Deposit transactions and cash management	40,000	38,000	78,000	77,000
Fixed income	0	0	0	0
Brokerage, management fees and commissions	22,000	24,000	44,000	48,000
Card and digital banking fees	19,000	21,000	36,000	38,000
Other service charges and fees	8,000	9,000	16,000	16,000
Trust services and investment management	12,000	12,000	24,000	25,000
Mortgage banking and title income	0	0	0	0
Deferred compensation income	0	0	0	0
Gain on merger termination	0		0
Securities gains (losses), net			0	0
Other income	7,000	10,000	17,000	24,000
Total noninterest income	108,000	114,000	215,000	228,000
Specialty Banking
Noninterest income:
Deposit transactions and cash management	3,000	2,000	5,000	5,000
Fixed income	31,000	51,000	70,000	124,000
Brokerage, management fees and commissions	0	0	0	0
Card and digital banking fees	0	0	1,000	1,000
Other service charges and fees	6,000	6,000	11,000	11,000
Trust services and investment management	0	0	0	0
Mortgage banking and title income	6,000	34,000	11,000	56,000
Deferred compensation income	0	0	0	0
Gain on merger termination	0		0
Securities gains (losses), net			0	0
Other income	2,000	3,000	3,000	4,000
Total noninterest income	48,000	96,000	101,000	201,000
Corporate
Noninterest income:
Deposit transactions and cash management	2,000	2,000	4,000	4,000
Fixed income	(1,000)	0	(1,000)	0
Brokerage, management fees and commissions	0	0	0	0
Card and digital banking fees	2,000	2,000	3,000	4,000
Other service charges and fees	0	0	0	1,000
Trust services and investment management	0	0	0	0
Mortgage banking and title income	0	0	0	0
Deferred compensation income	8,000	(17,000)	11,000	(21,000)
Gain on merger termination	225,000		225,000
Securities gains (losses), net			1,000	6,000
Other income	8,000	4,000	12,000	7,000
Total noninterest income	$ 244,000	$ (9,000)	$ 255,000	$ 1,000