Allowance for Credit Losses - Aging of Analysis of Past Due Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due
Total Past Due	$ 52,754	$ 58,126
Current	13,447,215	13,148,056
Total Accruing Loans and Leases		13,206,182
Total Non Accruing Loans and Leases		5,468
Total loans and leases	13,499,969	13,211,650
30 - 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	22,849	36,228
60 - 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	12,806	9,748
Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	17,099	12,150
Total Accruing Loans and Leases	10,745
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due
Total Past Due	6,107	3,762
Current	3,164,155	2,739,448
Total Accruing Loans and Leases		2,743,210
Total Non Accruing Loans and Leases		32
Total loans and leases	3,170,262	2,743,242
Commercial and Industrial | 30 - 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,233	1,525
Commercial and Industrial | 60 - 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,619	808
Commercial and Industrial | Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,255	1,429
Total Accruing Loans and Leases	1,938
Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,678	3,802
Current	3,458,407	3,460,121
Total Accruing Loans and Leases		3,463,923
Total Non Accruing Loans and Leases		30
Total loans and leases	3,461,085	3,463,953
Commercial real estate | 30 - 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	149	1,664
Commercial real estate | 60 - 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,142	1,125
Commercial real estate | Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	1,387	1,013
Total Accruing Loans and Leases	1,307
Construction
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,143	2,367
Current	660,728	516,874
Total Accruing Loans and Leases		519,241
Total loans and leases	662,871	519,241
Construction | Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,143	2,367
Total Accruing Loans and Leases	100
Lease financing
Financing Receivable, Recorded Investment, Past Due
Current	245,977	202,483
Total Accruing Loans and Leases		202,483
Total loans and leases	245,977	202,483
Residential
Financing Receivable, Recorded Investment, Past Due
Total loans and leases		4,662,175
Consumer
Financing Receivable, Recorded Investment, Past Due
Total loans and leases		1,620,556
Residential mortgage | Residential
Financing Receivable, Recorded Investment, Past Due
Total Past Due	5,403	3,731
Current	3,663,648	3,759,799
Total Accruing Loans and Leases		3,763,530
Total Non Accruing Loans and Leases		5,406
Total loans and leases	3,669,051	3,768,936
Residential mortgage | Residential | 30 - 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	921	3,258
Residential mortgage | Residential | 60 - 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	568	399
Residential mortgage | Residential | Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	3,914	74
Home equity | Home equity Line
Financing Receivable, Recorded Investment, Past Due
Total Past Due	9,877	6,360
Current	854,912	886,879
Total Accruing Loans and Leases		893,239
Total loans and leases	864,789	893,239
Home equity | Home equity Line | 30 - 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,837	2,971
Home equity | Home equity Line | 60 - 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,537	394
Home equity | Home equity Line | Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	4,503	2,995
Total Accruing Loans and Leases	4,503
Consumer loans
Financing Receivable, Recorded Investment, Past Due
Total loans and leases		226,304
Consumer loans | Consumer
Financing Receivable, Recorded Investment, Past Due
Total Past Due	26,546	38,104
Current	1,399,388	1,582,452
Total Accruing Loans and Leases		1,620,556
Total loans and leases	1,425,934	1,620,556
Consumer loans | Consumer | 30 - 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	17,709	26,810
Consumer loans | Consumer | 60 - 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	5,940	7,022
Consumer loans | Consumer | Greater Than or Equal to 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due
Total Past Due	2,897	$ 4,272
Total Accruing Loans and Leases	$ 2,897