Loans and Allowance for Credit Losses Past Due Loan Status and Non-Accrual Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Non- accrual	$ 138,833	$ 137,198
Total	18,269,407	18,900,820
Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	49,317	59,999
Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	6,249	20,321
Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	11,389	9,929
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	18,063,619	18,673,373
Real estate - commercial mortgage
Financing Receivable, Past Due [Line Items]
Non- accrual	48,134	51,470
Total	7,145,115	7,105,092
Real estate - commercial mortgage \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	7,495	14,999
Real estate - commercial mortgage \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	240	9,273
Real estate - commercial mortgage \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	3,966	1,177
Real estate - commercial mortgage \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	7,085,280	7,028,173
Commercial and industrial (1)
Financing Receivable, Past Due [Line Items]
Non- accrual	29,437	31,993
Total	4,454,059	5,670,828
Commercial and industrial (1) \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	16,134	11,285
Commercial and industrial (1) \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	1,366	1,068
Commercial and industrial (1) \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	3,261	616
Commercial and industrial (1) \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	4,403,861	5,625,866
Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
Non- accrual	35,381	26,107
Total	3,719,684	3,141,915
Real estate - residential mortgage \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	19,365	22,281
Real estate - residential mortgage \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	2,974	7,675
Real estate - residential mortgage \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	1,695	4,687
Real estate - residential mortgage \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	3,660,269	3,081,165
Real-estate - home equity
Financing Receivable, Past Due [Line Items]
Non- accrual	8,785	9,588
Total	1,126,628	1,202,913
Real-estate - home equity \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	3,245	5,622
Real-estate - home equity \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	1,194	1,654
Real-estate - home equity \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	2,286	2,753
Real-estate - home equity \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	1,111,118	1,183,296
Real-estate - construction
Financing Receivable, Past Due [Line Items]
Non- accrual	959	1,395
Total	1,111,487	1,047,218
Real-estate - construction \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	360	1,938
Real-estate - construction \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	0
Real-estate - construction \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	5	155
Real-estate - construction \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	1,110,163	1,043,730
Consumer
Financing Receivable, Past Due [Line Items]
Non- accrual	263	332
Total	458,595	466,772
Consumer \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	2,412	3,036
Consumer \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	475	501
Consumer \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	176	417
Consumer \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	455,269	462,486
Equipment lease financing, other and overdrafts
Financing Receivable, Past Due [Line Items]
Non- accrual	15,874	16,313
Total	253,839	266,082
Equipment lease financing, other and overdrafts \| Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	306	838
Equipment lease financing, other and overdrafts \| Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	150
Equipment lease financing, other and overdrafts \| Financial Asset, Equal to or Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total	0	124
Equipment lease financing, other and overdrafts \| Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total	$ 237,659	$ 248,657