Loans and Allowance for Credit Losses Loans Modified Under Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Accruing Troubled Debt Restructurings	$ 70,188	$ 55,150
Non-accrual TDRs (1)	37,025	20,825
Total TDRs	107,213	75,975
Loans and leases 90 days or more past due and still accruing	13,761	16,057
Financing Receivable, Nonaccrual	128,321	125,098
Financing Receivable, Not Past Due	18,845,238	16,620,575
Loans and Leases Receivable, Net of Deferred Income	19,028,621	16,837,526
Real estate - commercial mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases 90 days or more past due and still accruing	2,499	4,113
Financing Receivable, Nonaccrual	40,926	33,166
Financing Receivable, Not Past Due	6,987,336	6,651,042
Loans and Leases Receivable, Net of Deferred Income	7,046,330	6,700,776
Residential Mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Accruing Troubled Debt Restructurings	19,427	21,551
Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Accruing Troubled Debt Restructurings	28,558	13,330
Real-estate - home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Accruing Troubled Debt Restructurings	14,875	15,068
Loans and leases 90 days or more past due and still accruing	3,070	3,564
Financing Receivable, Nonaccrual	8,682	7,004
Financing Receivable, Not Past Due	1,206,089	1,292,035
Loans and Leases Receivable, Net of Deferred Income	1,222,709	1,314,944
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Accruing Troubled Debt Restructurings	7,328	5,193
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Accruing Troubled Debt Restructurings	0	8
Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Past Due	33,743	56,326
Financial Asset, 30 to 59 Days Past Due | Real estate - commercial mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Past Due	11,867	10,912
Financial Asset, 30 to 59 Days Past Due | Real-estate - home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Past Due	3,966	9,635
Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Past Due	7,558	19,470
Financial Asset, 60 to 89 Days Past Due | Real estate - commercial mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Past Due	3,702	1,543
Financial Asset, 60 to 89 Days Past Due | Real-estate - home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Past Due	$ 902	$ 2,706