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Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) - USD ($) $ in Thousands | Jun. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | $ 5,322,516 | $ 5,002,925
Total nonaccrual loans | 42,905 | 35,382
Total past due | 77,747 | 60,008
Total Loans | 5,400,263 | 5,062,933
Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 1,366,728 | 1,244,802
Total nonaccrual loans | 11,342 | 9,279
Total past due | 19,018 | 12,028
Total Loans | 1,385,746 | 1,256,830
Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 2,367,849 | 2,145,655
Total nonaccrual loans | 10,887 | 8,719
Total past due | 20,937 | 20,948
Total Loans | 2,388,786 | 2,166,603
Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 382,985 | 401,084
Total nonaccrual loans | 8,182 | 8,753
Total past due | 15,137 | 12,360
Total Loans | 398,122 | 413,444
Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 657,352 | 631,085
Total nonaccrual loans | 9,283 | 5,629
Total past due | 14,313 | 8,287
Total Loans | 671,665 | 639,372
Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 472,085 | 465,055
Total nonaccrual loans | 3,168 | 2,902
Total past due | 8,119 | 5,790
Total Loans | 480,204 | 470,845
Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 57,916 | 73,486
Total nonaccrual loans | 43 | 100
Total past due | 223 | 453
Total Loans | 58,139 | 73,939
Consumer Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 5,602 | 6,579
Total nonaccrual loans | 0 | 0
Total past due | 0 | 0
Total Loans | 5,602 | 6,579
Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 11,999 | 35,179
Total nonaccrual loans | 0 | 0
Total past due | 0 | 142
Total Loans | 11,999 | 35,321
30 to 59 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 25,871 | 22,001
30 to 59 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 7,276 | 2,453
30 to 59 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 7,384 | 11,602
30 to 59 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 5,644 | 3,517
30 to 59 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 1,191 | 1,728
30 to 59 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 4,223 | 2,365
30 to 59 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 153 | 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 | 8,971 | 2,625
60 to 89 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 400 | 296
60 to 89 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 2,666 | 627
60 to 89 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 1,311 | 90
60 to 89 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,839 | 930
60 to 89 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 728 | 523
60 to 89 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 27 | 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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