Allowance for Credit Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)
Financing Receivable, Past Due [Line Items]
Current	$ 7,069,730	$ 7,055,361
Past Due	156,130	81,791
Non- performing	146,774	54,057
Total	7,225,860	7,137,152
Restructured loans	$ 22,650	32,206
CARES Act, Paycheck Protection Program Loans
Financing Receivable, Past Due [Line Items]
Number of modified loans | loan	52
CARES Act, Paycheck Protection Program Loans
Financing Receivable, Past Due [Line Items]
Restructured loans	$ 195,600
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	2,888	17,992
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	5,965	5,985
90 Days Past Due
Financing Receivable, Past Due [Line Items]
Past Due	503	3,757
Commercial
Financing Receivable, Past Due [Line Items]
Total	5,977,643	5,756,971
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Current	2,690,877	3,025,505
Past Due	101,070	34,087
Non- performing	101,070	25,356
Total	2,791,947	3,059,592	$ 3,416,518
Restructured loans	4,791	25,159
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Current	1,542,567	1,466,460
Past Due	16,985	14,069
Non- performing	16,985	10,911
Total	1,559,552	1,480,529	1,720,833
Restructured loans	13,716	5,661
Commercial | Other Consumer
Financing Receivable, Past Due [Line Items]
Current	462,094	367,204
Past Due	3,983	2,856
Non- performing	384	737
Total	466,077	370,060	375,445
Restructured loans	2,329
Commercial | Business banking
Financing Receivable, Past Due [Line Items]
Current	1,140,581	830,735
Past Due	19,486	16,055
Non- performing	17,122	9,863
Total	1,160,067	846,790	0
Restructured loans	165
Commercial | 30-59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Past Due	0	7,749
Commercial | 30-59 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Past Due	0	126
Commercial | 30-59 Days Past Due | Other Consumer
Financing Receivable, Past Due [Line Items]
Past Due	19	956
Commercial | 30-59 Days Past Due | Business banking
Financing Receivable, Past Due [Line Items]
Past Due	1,614	5,093
Commercial | 60-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Past Due	0	71
Commercial | 60-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Past Due	0	1,589
Commercial | 60-89 Days Past Due | Other Consumer
Financing Receivable, Past Due [Line Items]
Past Due	3,580	1,163
Commercial | 60-89 Days Past Due | Business banking
Financing Receivable, Past Due [Line Items]
Past Due	379	1,099
Commercial | 90 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Past Due	0	911
Commercial | 90 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Past Due	0	1,443
Commercial | 90 Days Past Due | Other Consumer
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Commercial | 90 Days Past Due | Business banking
Financing Receivable, Past Due [Line Items]
Past Due	371	0
Consumer
Financing Receivable, Past Due [Line Items]
Total	1,248,217	1,380,181
Consumer | Other Consumer
Financing Receivable, Past Due [Line Items]
Total		8,390
Consumer | Consumer real estate
Financing Receivable, Past Due [Line Items]
Current	1,153,028	1,283,591
Past Due	14,304	11,616
Non- performing	11,117	6,063
Total	1,167,332	1,295,207	1,545,323
Restructured loans	1,645
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Current	80,583	81,866
Past Due	302	3,108
Non- performing	96	1,127
Total	80,885	84,974	$ 79,033
Restructured loans	4
Consumer | 30-59 Days Past Due | Consumer real estate
Financing Receivable, Past Due [Line Items]
Past Due	1,087	2,620
Consumer | 30-59 Days Past Due | Other consumer
Financing Receivable, Past Due [Line Items]
Past Due	168	1,448
Consumer | 60-89 Days Past Due | Consumer real estate
Financing Receivable, Past Due [Line Items]
Past Due	1,968	1,758
Consumer | 60-89 Days Past Due | Other consumer
Financing Receivable, Past Due [Line Items]
Past Due	37	305
Consumer | 90 Days Past Due | Consumer real estate
Financing Receivable, Past Due [Line Items]
Past Due	132	1,175
Consumer | 90 Days Past Due | Other consumer
Financing Receivable, Past Due [Line Items]
Past Due	$ 0	$ 228