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Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | $ 5,372,840 | $ 5,002,925
Total nonaccrual loans | 40,493 | 35,382
Total past due | 57,088 | 60,008
Total Loans | 5,429,928 | 5,062,933
Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 1,327,898 | 1,244,802
Total nonaccrual loans | 11,890 | 9,279
Total past due | 16,399 | 12,028
Total Loans | 1,344,297 | 1,256,830
Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 2,413,004 | 2,145,655
Total nonaccrual loans | 7,551 | 8,719
Total past due | 14,160 | 20,948
Total Loans | 2,427,164 | 2,166,603
Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 394,812 | 401,084
Total nonaccrual loans | 6,653 | 8,753
Total past due | 7,312 | 12,360
Total Loans | 402,124 | 413,444
Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 679,237 | 631,085
Total nonaccrual loans | 11,400 | 5,629
Total past due | 13,337 | 8,287
Total Loans | 692,574 | 639,372
Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 478,389 | 465,055
Total nonaccrual loans | 2,955 | 2,902
Total past due | 5,546 | 5,790
Total Loans | 483,935 | 470,845
Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 61,954 | 73,486
Total nonaccrual loans | 44 | 100
Total past due | 334 | 453
Total Loans | 62,288 | 73,939
Consumer Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 5,852 | 6,579
Total nonaccrual loans | 0 | 0
Total past due | 0 | 0
Total Loans | 5,852 | 6,579
Loans Held for Sale |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Loans, Current | 11,694 | 35,179
Total nonaccrual loans | 0 | 0
Total past due | 0 | 142
Total Loans | 11,694 | 35,321
30 to 59 Days Past Due |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 10,389 | 22,001
30 to 59 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,536 | 2,453
30 to 59 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,286 | 11,602
30 to 59 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 456 | 3,517
30 to 59 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 585 | 1,728
30 to 59 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 2,321 | 2,365
30 to 59 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 205 | 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 | 6,206 | 2,625
60 to 89 Days Past Due | Commercial and Industrial |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 973 | 296
60 to 89 Days Past Due | Commercial Real Estate |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 3,323 | 627
60 to 89 Days Past Due | Commercial Construction |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 203 | 90
60 to 89 Days Past Due | Residential Mortgage |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 1,352 | 930
60 to 89 Days Past Due | Home Equity |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 270 | 523
60 to 89 Days Past Due | Installment and Other Consumer |  |
Financing Receivable, Recorded Investment, Past Due [Line Items] |  |
Total past due | 85 | 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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