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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, 2017 | Dec. 31, 2016
--- | --- | ---
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | $ 5,829,789 | $ 5,563,123
Total nonaccrual loans | 29,493 | 42,635
Total past due | 38,905 | 52,089
Total Loans | 5,868,694 | 5,615,212
Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 2,674,171 | 2,479,513
Total nonaccrual loans | 6,571 | 16,172
Total past due | 7,522 | 18,963
Total Loans | 2,681,693 | 2,498,476
Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 1,438,224 | 1,391,475
Total nonaccrual loans | 7,349 | 8,071
Total past due | 8,587 | 9,560
Total Loans | 1,446,811 | 1,401,035
Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 428,744 | 450,410
Total nonaccrual loans | 4,068 | 4,927
Total past due | 4,143 | 5,474
Total Loans | 432,887 | 455,884
Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 684,848 | 689,635
Total nonaccrual loans | 7,782 | 9,918
Total past due | 12,519 | 12,347
Total Loans | 697,367 | 701,982
Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 482,000 | 476,866
Total nonaccrual loans | 3,675 | 3,439
Total past due | 5,806 | 5,418
Total Loans | 487,806 | 482,284
Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 69,316 | 65,525
Total nonaccrual loans | 48 | 108
Total past due | 328 | 327
Total Loans | 69,644 | 65,852
Consumer Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 4,550 | 5,906
Total nonaccrual loans | 0 | 0
Total past due | 0 | 0
Total Loans | 4,550 | 5,906
Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 47,936 | 3,793
Total nonaccrual loans | 0 | 0
Total past due | 0 | 0
Total Loans | 47,936 | 3,793
30 to 59 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 6,820 | 6,598
30 to 59 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 530 | 2,032
30 to 59 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 499 | 1,061
30 to 59 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 75 | 547
30 to 59 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,872 | 1,312
30 to 59 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 1,616 | 1,470
30 to 59 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 228 | 176
30 to 59 Days Past Due | Consumer Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 0 | 0
30 to 59 Days Past Due | Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 0 | 0
60 to 89 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 2,592 | 2,856
60 to 89 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 421 | 759
60 to 89 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 739 | 428
60 to 89 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 0 | 0
60 to 89 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 865 | 1,117
60 to 89 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 515 | 509
60 to 89 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 52 | 43
60 to 89 Days Past Due | Consumer Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 0 | 0
60 to 89 Days Past Due | Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | $ 0 | $ 0

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