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Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract] |  |  |
Tax at statutory rate, Amount | $ 36,304 | $ 29,830 | $ 24,843
Income Tax Reconciliation, Bank Owned Life Insurance Income | (1,995) | (1,883) | (1,894)
Tax-exempt interest income, net, Amount | (2,709) | (2,434) | (2,232)
Tax credits, Amount | (11) | 0 | (61)
Other, Amount | 99 | 182 | 136
Total tax provision (benefit), Amount | $ 48,561 | $ 25,639 | $ 20,836
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract] |  |  |
Tax at statutory rate, Pretax Income | 35.00% | 35.00% | 35.00%
Income from bank owned life insurance, Pretax Income | (2.00%) | (2.00%) | (3.00%)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount | $ 164 | $ (56) | $ 44
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent | 0.00% | 0.00% | 0.00%
Tax-exempt interest income, net, Pretax Income | (3.00%) | (3.00%) | (3.00%)
Tax credits, Pretax Income | (0.00%) | (0.00%) | (0.00%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount | $ 16,709 | $ 0 | $ 0
Effective Income Tax Rate Reconciliation, Deduction, Percent | (17.00%) | 0.00% | 0.00%
Other, Pretax Income | 0.00% | 0.00% | 0.00%
Total tax provision (benefit), Pretax Income | 47.00% | 30.00% | 29.00%

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