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Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) - USD ($) $ in Thousands | Mar. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | $ 5,102,365 | $ 5,002,925
Total nonaccrual loans | 51,834 | 35,382
Total past due | 86,122 | 60,008
Total Loans | 5,188,487 | 5,062,933
Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 2,238,144 | 2,145,655
Total nonaccrual loans | 15,244 | 8,719
Total past due | 22,087 | 20,948
Total Loans | 2,260,231 | 2,166,603
Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 1,306,834 | 1,244,802
Total nonaccrual loans | 14,209 | 9,279
Total past due | 27,285 | 12,028
Total Loans | 1,334,119 | 1,256,830
Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 364,675 | 401,084
Total nonaccrual loans | 9,993 | 8,753
Total past due | 14,618 | 12,360
Total Loans | 379,293 | 413,444
Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 636,328 | 631,085
Total nonaccrual loans | 9,012 | 5,629
Total past due | 14,216 | 8,287
Total Loans | 650,544 | 639,372
Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 460,203 | 465,055
Total nonaccrual loans | 3,267 | 2,902
Total past due | 7,468 | 5,790
Total Loans | 467,671 | 470,845
Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 75,741 | 73,486
Total nonaccrual loans | 109 | 100
Total past due | 448 | 453
Total Loans | 76,189 | 73,939
Consumer Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 8,701 | 6,579
Total nonaccrual loans | 0 | 0
Total past due | 0 | 0
Total Loans | 8,701 | 6,579
Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 11,739 | 35,179
Total nonaccrual loans | 0 | 0
Total past due | 0 | 142
Total Loans | 11,739 | 35,321
30 to 59 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 26,064 | 22,001
30 to 59 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 6,669 | 11,602
30 to 59 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 12,509 | 2,453
30 to 59 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 1,086 | 3,517
30 to 59 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 1,749 | 1,728
30 to 59 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,754 | 2,365
30 to 59 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 297 | 242
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 | 94
60 to 89 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 8,224 | 2,625
60 to 89 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 174 | 627
60 to 89 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 567 | 296
60 to 89 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,539 | 90
60 to 89 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,455 | 930
60 to 89 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 447 | 523
60 to 89 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 42 | 111
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 | $ 48

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