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Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | $ 5,730,074 | $ 5,563,123
Past Due | 35,860 | 52,089
Non- performing | 23,938 | 42,635
Total Loans | 5,765,934 | 5,615,212
Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 2,681,395 | 2,479,513
Past Due | 4,599 | 18,963
Total Loans | 2,685,994 | 2,498,476
Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 1,426,754 | 1,391,475
Past Due | 6,512 | 9,560
Total Loans | 1,433,266 | 1,401,035
Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 377,968 | 450,410
Past Due | 6,366 | 5,474
Total Loans | 384,334 | 455,884
Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 687,195 | 689,635
Past Due | 11,579 | 12,347
Total Loans | 698,774 | 701,982
Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 480,956 | 476,866
Past Due | 6,370 | 5,418
Total Loans | 487,326 | 482,284
Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 66,770 | 65,525
Past Due | 434 | 327
Total Loans | 67,204 | 65,852
Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 4,551 | 5,906
Past Due | 0 | 0
Total Loans | 4,551 | 5,906
Loans held for sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Current | 4,485 | 3,793
Past Due | 0 | 0
Total Loans | 4,485 | 3,793
30-59 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 9,123 | 6,598
30-59 Days Past Due | Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 997 | 2,032
30-59 Days Past Due | Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 420 | 1,061
30-59 Days Past Due | Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 2,473 | 547
30-59 Days Past Due | Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 2,975 | 1,312
30-59 Days Past Due | Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 2,065 | 1,470
30-59 Days Past Due | Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 193 | 176
30-59 Days Past Due | Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 0 | 0
30-59 Days Past Due | Loans held for sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 0 | 0
60-89 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 2,799 | 2,856
60-89 Days Past Due | Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 134 | 759
60-89 Days Past Due | Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 446 | 428
60-89 Days Past Due | Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 20 | 0
60-89 Days Past Due | Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 1,439 | 1,117
60-89 Days Past Due | Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 590 | 509
60-89 Days Past Due | Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 170 | 43
60-89 Days Past Due | Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 0 | 0
60-89 Days Past Due | Loans held for sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Past Due | 0 | 0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 23,938 | 42,635
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial real estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 3,468 | 16,172
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial and industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 5,646 | 8,071
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 3,873 | 4,927
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 7,165 | 9,918
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Home equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 3,715 | 3,439
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Installment and other consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 71 | 108
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | 0 | 0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Loans held for sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Non- performing | $ 0 | $ 0

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