Loans and Allowance for Credit Losses Past Due Loan Status and Non-Accrual Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	$ 19,593	$ 16,057
Non- accrual	120,345	125,098
Current	16,866,683	16,620,575
Net loans	17,077,403	16,837,526	$ 16,262,633
Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	55,773	56,326
Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	15,009	19,470
Real-estate - commercial mortgage
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	879	4,113
Non- accrual	35,657	33,166
Current	6,837,453	6,651,042
Net loans	6,895,069	6,700,776	6,428,688
Real-estate - commercial mortgage | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	20,052	10,912
Real-estate - commercial mortgage | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	1,028	1,543
Commercial and industrial
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	243	1,385
Non- accrual	41,075	48,106
Current	4,401,943	4,392,278
Net loans	4,451,239	4,446,701	4,429,538
Commercial and industrial | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	3,401	2,302
Commercial and industrial | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	4,577	2,630
Real-estate - home equity
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	3,525	3,564
Non- accrual	7,261	7,004
Current	1,273,110	1,292,035
Net loans	1,292,677	1,314,944	1,413,500
Real-estate - home equity | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	6,782	9,635
Real-estate - home equity | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	1,999	2,706
Real estate - residential mortgage
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	9,439	5,735
Non- accrual	16,393	16,676
Current	2,665,055	2,584,763
Net loans	2,718,290	2,641,465	2,313,908
Real estate - residential mortgage | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	21,052	26,982
Real estate - residential mortgage | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	6,351	7,309
Real estate - construction
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	820	688
Non- accrual	3,560	3,618
Current	942,910	964,158
Net loans	947,768	971,079	953,087
Real estate - construction | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	173	1,715
Real estate - construction | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	305	900
Consumer
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	440	458
Non- accrual	0	0
Current	464,325	457,556
Net loans	468,172	463,164	433,545
Consumer | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	2,852	4,228
Consumer | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	555	922
Equipment lease financing, other and overdrafts
Financing Receivable, Past Due [Line Items]
≥ 90 Days Past Due and Accruing	4,247	114
Non- accrual	16,399	16,528
Current	281,887	278,743
Net loans	304,188	299,397	$ 290,367
Equipment lease financing, other and overdrafts | Financial Asset, 30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	1,461	552
Equipment lease financing, other and overdrafts | Financial Asset, 60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-accrual	$ 194	$ 3,460