Business Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Fixed income	$ 77,645	$ 44,813	$ 197,808	$ 128,016
Gain On Sale Of Held To Maturity Loans			1,105	(3,777)
Deposit transactions and cash management	34,379	35,792	98,374	107,859
Brokerage, management fees and commissions	14,157	14,200	40,910	41,423
Trust services and investment management	7,163	7,438	22,077	22,847
Bankcard income	7,017	7,744	20,324	21,734
Bank-owned life insurance (BOLI)	4,427	4,337	13,955	14,103
Debt securities gains/(losses), net	0	0	(267)	52
Equity securities gains/(losses), net	97	212,859	444	212,924
All other income and commissions (Note 8)	26,850	21,789	77,148	63,556
Total noninterest income	171,735	348,972	470,773	612,514
Gains on the sales of buildings			(20,453)	2,469
Regional Banking
Disaggregation of Revenue [Line Items]
Fixed income	57	102	120	314
Deposit transactions and cash management	32,583	33,989	93,195	103,219
Brokerage, management fees and commissions	14,157	14,199	40,904	41,422
Trust services and investment management	7,190	7,453	22,148	22,891
Bankcard income	7,028	7,865	20,661	21,696
Bank-owned life insurance (BOLI)	0	0	0	0
Debt securities gains/(losses), net	0	0	0	0
Equity securities gains/(losses), net	0	0	0	0
All other income and commissions (Note 8)	24,761	17,097	63,253	52,218
Total noninterest income	85,776	80,705	240,281	241,760
Fixed Income
Disaggregation of Revenue [Line Items]
Fixed income	77,588	40,938	196,582	123,929
Deposit transactions and cash management	0	3	4	9
Brokerage, management fees and commissions	0	0	0	0
Trust services and investment management	0	0	0	0
Bankcard income	11	0	11	0
Bank-owned life insurance (BOLI)	0	0	0	0
Debt securities gains/(losses), net	0	0	0	0
Equity securities gains/(losses), net	0	0	0	0
All other income and commissions (Note 8)	210	183	641	1,153
Total noninterest income	77,809	41,124	197,238	125,091
Corporate
Disaggregation of Revenue [Line Items]
Fixed income	0	(5)	0	(5)
Deposit transactions and cash management	1,739	1,741	5,009	4,467
Brokerage, management fees and commissions	0	0	0	0
Trust services and investment management	(27)	(15)	(71)	(44)
Bankcard income	63	57	185	169
Bank-owned life insurance (BOLI)	4,427	4,337	13,955	14,103
Debt securities gains/(losses), net	0	0	(267)	52
Equity securities gains/(losses), net	97	212,859	444	212,924
All other income and commissions (Note 8)	1,060	3,646	10,856	9,008
Total noninterest income	7,359	222,620	30,111	240,674
Gains on the sales of buildings				4,100
Non-Strategic
Disaggregation of Revenue [Line Items]
Fixed income	0	3,778	1,106	3,778
Gain On Sale Of Held To Maturity Loans		3,800		3,800
Deposit transactions and cash management	57	59	166	164
Brokerage, management fees and commissions	0	1	6	1
Trust services and investment management	0	0	0	0
Bankcard income	(85)	(178)	(533)	(131)
Bank-owned life insurance (BOLI)	0	0	0	0
Debt securities gains/(losses), net	0	0	0	0
Equity securities gains/(losses), net	0	0	0	0
All other income and commissions (Note 8)	819	863	2,398	1,177
Total noninterest income	791	4,523	3,143	4,989
Underwriting, Portfolio Advisory, and Other Noninterest Income
Disaggregation of Revenue [Line Items]
Fixed income	$ 9,200	8,400	$ 23,600	24,000
Visa Class B Shares
Disaggregation of Revenue [Line Items]
Gain on sale of investments		$ 212,900		$ 212,900