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Segments - Financial Information of Segments (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest income | $ 53,353 | $ 53,669 | $ 52,611 | $ 43,916 | $ 41,381 | $ 40,605 | $ 39,872 | $ 38,665 | $ 203,548 | $ 160,523 | $ 153,756
Interest expense | 4,468 | 4,073 | 3,800 | 3,657 | 3,315 | 3,076 | 3,017 | 3,074 | 15,997 | 12,481 | 14,563
NET INTEREST INCOME |  |  |  |  |  |  |  |  | 187,551 | 148,042 | 139,193
Provision for loan losses | 3,915 | 3,206 | 2,059 | 1,207 | 1,106 | 1,454 | (1,134) | 289 | 10,388 | 1,715 | 8,311
Noninterest income | 13,084 | 12,481 | 13,417 | 12,084 | 11,220 | 11,931 | 11,731 | 11,415 | 51,033 | 46,338 | 51,527
Noninterest Expense | 33,817 | 33,829 | 35,449 | 33,621 | 29,720 | 28,440 | 30,165 | 28,914 | 136,717 | 117,240 | 117,392
Noninterest expense |  |  |  |  |  |  |  |  | 130,160 | 112,646 | 112,294
Depreciation expense |  |  |  |  |  |  |  |  | 4,739 | 3,465 | 3,507
Amortization of intangible assets |  |  |  |  |  |  |  |  | 1,818 | 1,129 | 1,591
Provision (benefit) for income taxes | $ 6,814 | $ 6,407 | $ 6,498 | $ 4,680 | $ 3,963 | $ 4,906 | $ 4,875 | $ 3,771 | 24,398 | 17,515 | 14,478
Net Income |  |  |  |  |  |  |  |  | 67,081 | 57,910 | 50,539
Operating Segments | Community Banking |  |  |  |  |  |  |  |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest income |  |  |  |  |  |  |  |  | 203,439 | 160,403 | 153,450
Interest expense |  |  |  |  |  |  |  |  | 16,678 | 13,989 | 16,508
NET INTEREST INCOME |  |  |  |  |  |  |  |  | 186,761 | 146,414 | 136,942
Provision for loan losses |  |  |  |  |  |  |  |  | 10,388 | 1,715 | 8,311
Noninterest income |  |  |  |  |  |  |  |  | 34,106 | 29,443 | 34,649
Noninterest expense |  |  |  |  |  |  |  |  | 115,998 | 97,733 | 94,769
Depreciation expense |  |  |  |  |  |  |  |  | 4,664 | 3,387 | 3,430
Amortization of intangible assets |  |  |  |  |  |  |  |  | 1,738 | 1,039 | 1,492
Provision (benefit) for income taxes |  |  |  |  |  |  |  |  | 23,209 | 16,311 | 14,180
Net Income |  |  |  |  |  |  |  |  | 64,870 | 55,672 | 49,409
Operating Segments | Insurance |  |  |  |  |  |  |  |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest income |  |  |  |  |  |  |  |  | 2 | 2 | 2
Interest expense |  |  |  |  |  |  |  |  | 0 | 0 | 0
NET INTEREST INCOME |  |  |  |  |  |  |  |  | 2 | 2 | 2
Provision for loan losses |  |  |  |  |  |  |  |  | 0 | 0 | 0
Noninterest income |  |  |  |  |  |  |  |  | 5,035 | 5,279 | 5,483
Noninterest expense |  |  |  |  |  |  |  |  | 4,365 | 4,313 | 5,210
Depreciation expense |  |  |  |  |  |  |  |  | 50 | 51 | 47
Amortization of intangible assets |  |  |  |  |  |  |  |  | 50 | 51 | 51
Provision (benefit) for income taxes |  |  |  |  |  |  |  |  | 200 | 303 | (47)
Net Income |  |  |  |  |  |  |  |  | 372 | 563 | 224
Operating Segments | Wealth Management |  |  |  |  |  |  |  |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest income |  |  |  |  |  |  |  |  | 508 | 518 | 517
Interest expense |  |  |  |  |  |  |  |  | 0 | 0 | 0
NET INTEREST INCOME |  |  |  |  |  |  |  |  | 508 | 518 | 517
Provision for loan losses |  |  |  |  |  |  |  |  | 0 | 0 | 0
Noninterest income |  |  |  |  |  |  |  |  | 11,412 | 11,297 | 10,662
Noninterest expense |  |  |  |  |  |  |  |  | 9,037 | 9,173 | 9,850
Depreciation expense |  |  |  |  |  |  |  |  | 25 | 27 | 30
Amortization of intangible assets |  |  |  |  |  |  |  |  | 30 | 39 | 48
Provision (benefit) for income taxes |  |  |  |  |  |  |  |  | 989 | 901 | 345
Net Income |  |  |  |  |  |  |  |  | 1,839 | 1,675 | 906
Eliminations |  |  |  |  |  |  |  |  |  |  |
Segment Reporting, Asset Reconciling Item [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest income |  |  |  |  |  |  |  |  | (401) | (400) | (213)
Interest expense |  |  |  |  |  |  |  |  | (681) | (1,508) | (1,945)
NET INTEREST INCOME |  |  |  |  |  |  |  |  | 280 | 1,108 | 1,732
Provision for loan losses |  |  |  |  |  |  |  |  | 0 | 0 | 0
Noninterest income |  |  |  |  |  |  |  |  | 480 | 319 | 733
Noninterest expense |  |  |  |  |  |  |  |  | 760 | 1,427 | 2,465
Depreciation expense |  |  |  |  |  |  |  |  | 0 | 0 | 0
Amortization of intangible assets |  |  |  |  |  |  |  |  | 0 | 0 | 0
Provision (benefit) for income taxes |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net Income |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 0

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