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Allowance for Credit Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) $ in Thousands | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 USD ($) loan | Sep. 30, 2019 USD ($) loan | Sep. 30, 2020 USD ($) loan | Sep. 30, 2019 USD ($) loan | Jan. 01, 2020 USD ($) | Dec. 31, 2019 USD ($)
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | $ 7,302,311 |  | $ 7,302,311 |  |  | $ 7,055,361
Past due | 92,556 |  | 92,556 |  |  | 81,791
Non - performing | 84,072 |  | 84,072 |  |  | 54,057
Total | $ 7,394,868 |  | $ 7,394,868 |  |  | 7,137,152
Number of loans | loan | 14 | 22 | 34 | 46 |  |
Restructured loans | $ 4,562 | $ 25,800 | $ 11,586 | $ 36,712 |  |
CARES Act, Paycheck Protection Program Loans |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Restructured loans |  |  | 350,000 |  |  |
30 to 59 Days Past Due |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 6,040 |  | 6,040 |  |  | 17,992
60 to 89 Days Past Due |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 1,925 |  | 1,925 |  |  | 5,985
90 Days Past Due |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 520 |  | 520 |  |  | 3,757
Commercial |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Total | 5,810,034 |  | 5,810,034 |  |  | 5,512,796
Commercial | Commercial real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | 2,771,132 |  | 2,771,132 |  |  | 3,025,505
Past due | 47,095 |  | 47,095 |  |  | 34,087
Non - performing | 47,095 |  | 47,095 |  |  | 25,356
Total | $ 2,818,227 |  | $ 2,818,227 |  | $ 3,416,518 | 3,059,592
Number of loans | loan | 1 | 5 | 2 | 8 |  |
Restructured loans | $ 171 | $ 23,784 | $ 2,381 | $ 29,747 |  |
Commercial | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | 1,811,342 |  | 1,811,342 |  |  | 1,466,460
Past due | 7,307 |  | 7,307 |  |  | 14,069
Non - performing | 5,686 |  | 5,686 |  |  | 10,911
Total | $ 1,818,649 |  | $ 1,818,649 |  | 1,720,833 | 1,480,529
Number of loans | loan | 2 | 2 | 5 | 3 |  |
Restructured loans | $ 4,022 | $ 1,527 | $ 5,381 | $ 5,860 |  |
Commercial | Commercial construction |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | 469,356 |  | 469,356 |  |  | 367,204
Past due | 1,504 |  | 1,504 |  |  | 2,856
Non - performing | 1,504 |  | 1,504 |  |  | 737
Total | $ 470,860 |  | $ 470,860 |  | 375,445 | 370,060
Number of loans | loan | 0 |  | 3 |  |  |
Restructured loans | $ 0 |  | $ 2,561 |  |  |
Commercial | Business banking |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | 994,389 |  | 994,389 |  |  | 830,735
Past due | 21,562 |  | 21,562 |  |  | 16,055
Non - performing | 18,081 |  | 18,081 |  |  | 9,863
Total | 1,015,951 |  | 1,015,951 |  | 0 | 846,790
Commercial | 30 to 59 Days Past Due | Commercial real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 7,749
Commercial | 30 to 59 Days Past Due | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 1,235 |  | 1,235 |  |  | 126
Commercial | 30 to 59 Days Past Due | Commercial construction |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 956
Commercial | 30 to 59 Days Past Due | Business banking |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 2,733 |  | 2,733 |  |  | 5,093
Commercial | 60 to 89 Days Past Due | Commercial real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 71
Commercial | 60 to 89 Days Past Due | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 1,589
Commercial | 60 to 89 Days Past Due | Commercial construction |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 1,163
Commercial | 60 to 89 Days Past Due | Business banking |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 748 |  | 748 |  |  | 1,099
Commercial | 90 Days Past Due | Commercial real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 911
Commercial | 90 Days Past Due | Commercial and industrial |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 386 |  | 386 |  |  | 1,443
Commercial | 90 Days Past Due | Commercial construction |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due |  |  |  |  |  | 0
Commercial | 90 Days Past Due | Business banking |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 0 |  | 0 |  |  | 0
Consumer |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Total | 1,584,834 |  | 1,584,834 |  |  | 1,624,356
Consumer | Commercial construction |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Total | 15,343 |  | 15,343 |  |  | 8,390
Consumer | Consumer real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | 1,177,782 |  | 1,177,782 |  |  | 1,283,591
Past due | 12,698 |  | 12,698 |  |  | 11,616
Non - performing | 9,810 |  | 9,810 |  |  | 6,063
Total | 1,190,480 |  | 1,190,480 |  | 1,545,323 | 1,295,207
Consumer | Other consumer |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Current | 78,310 |  | 78,310 |  |  | 81,866
Past due | 2,391 |  | 2,391 |  |  | 3,108
Non - performing | 1,896 |  | 1,896 |  |  | 1,127
Total | 80,701 |  | 80,701 |  | $ 79,033 | 84,974
Consumer | 30 to 59 Days Past Due | Consumer real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 1,723 |  | 1,723 |  |  | 2,620
Consumer | 30 to 59 Days Past Due | Other consumer |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 349 |  | 349 |  |  | 1,448
Consumer | 60 to 89 Days Past Due | Consumer real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 1,031 |  | 1,031 |  |  | 1,758
Consumer | 60 to 89 Days Past Due | Other consumer |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 146 |  | 146 |  |  | 305
Consumer | 90 Days Past Due | Consumer real estate |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | 134 |  | 134 |  |  | 1,175
Consumer | 90 Days Past Due | Other consumer |  |  |  |  |  |
Financing Receivable, Past Due [Line Items] |  |  |  |  |  |
Past due | $ 0 |  | $ 0 |  |  | $ 228

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