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Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax at statutory rate, Amount	$ 27,882	$ 36,304	$ 29,830
Income Tax Reconciliation, Bank Owned Life Insurance Income	(1,404)	(1,995)	(1,883)
Tax-exempt interest income, net, Amount	(1,473)	(2,709)	(2,434)
Tax credits, Amount	(5)	(11)	0
Other, Amount	400	99	182
Total tax provision (benefit), Amount	$ 25,274	$ 48,561	$ 25,639
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Tax at statutory rate, Pretax Income	21.00%	35.00%	35.00%
Income from bank owned life insurance, Pretax Income	(1.00%)	(2.00%)	(2.00%)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	$ 220	$ 164	$ (56)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	0.00%	0.00%	0.00%
Tax-exempt interest income, net, Pretax Income	(1.00%)	(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	$ (346)	$ (16,709)	$ 0
Effective Income Tax Rate Reconciliation, Deduction, Percent	0.00%	(17.00%)	0.00%
Other, Pretax Income	0.00%	0.00%	0.00%
Total tax provision (benefit), Pretax Income	19.00%	47.00%	30.00%

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