Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax at statutory rate, Amount	$ 18,943	$ 27,478	$ 27,882
Income Tax Reconciliation, Bank Owned Life Insurance Income	(1,376)	(1,260)	(1,404)
Tax-exempt interest income, net, Amount	(1,117)	(1,298)	(1,473)
Tax credits, Amount	(44)	(7)	(5)
Other, Amount	195	374	400
Total tax provision (benefit), Amount	$ 16,756	$ 25,516	$ 25,274
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Tax at statutory rate, Pretax Income	21.00%	21.00%	21.00%
Income from bank owned life insurance, Pretax Income	(1.00%)	(1.00%)	(1.00%)
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	$ 155	$ 229	$ 220
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%)	(1.00%)	(1.00%)
Tax credits, Pretax Income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0	$ 0	$ (346)
Effective Income Tax Rate Reconciliation, Deduction, Percent	0.00%	0.00%	0.00%
Other, Pretax Income	0.00%	0.00%	0.00%
Total tax provision (benefit), Pretax Income	19.00%	19.00%	19.00%