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Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | $ 5,781,619 | $ 5,730,074
Non - performing | 20,739 | 23,938
Past due | 30,395 | 35,860
Total Loans | 5,812,014 | 5,765,934
Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 2,820,689 | 2,681,395
Non - performing | 4,595 | 3,468
Past due | 5,683 | 4,599
Total Loans | 2,826,372 | 2,685,994
Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 1,445,433 | 1,426,754
Non - performing | 4,367 | 5,646
Past due | 5,938 | 6,512
Total Loans | 1,451,371 | 1,433,266
Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 282,489 | 377,968
Non - performing | 1,228 | 3,873
Past due | 1,294 | 6,366
Total Loans | 283,783 | 384,334
Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 689,464 | 687,195
Non - performing | 6,721 | 7,165
Past due | 10,403 | 11,579
Total Loans | 699,867 | 698,774
Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 465,625 | 480,956
Non - performing | 3,783 | 3,715
Past due | 6,826 | 6,370
Total Loans | 472,451 | 487,326
Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 67,291 | 66,770
Non - performing | 45 | 71
Past due | 251 | 434
Total Loans | 67,542 | 67,204
Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 6,421 | 4,551
Non - performing | 0 | 0
Past due | 0 | 0
Total Loans | 6,421 | 4,551
Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 4,207 | 4,485
Non - performing | 0 | 0
Past due | 0 | 0
Total Loans | 4,207 | 4,485
30 to 59 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 7,097 | 9,123
30 to 59 Days Past Due | Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 664 | 997
30 to 59 Days Past Due | Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 1,400 | 420
30 to 59 Days Past Due | Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 66 | 2,473
30 to 59 Days Past Due | Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 2,242 | 2,975
30 to 59 Days Past Due | Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 2,590 | 2,065
30 to 59 Days Past Due | Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 135 | 193
30 to 59 Days Past Due | Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 0 | 0
30 to 59 Days Past Due | Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 0 | 0
60 to 89 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 2,559 | 2,799
60 to 89 Days Past Due | Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 424 | 134
60 to 89 Days Past Due | Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 171 | 446
60 to 89 Days Past Due | Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 0 | 20
60 to 89 Days Past Due | Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 1,440 | 1,439
60 to 89 Days Past Due | Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 453 | 590
60 to 89 Days Past Due | Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 71 | 170
60 to 89 Days Past Due | Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | 0 | 0
60 to 89 Days Past Due | Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past due | $ 0 | $ 0

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