Income Taxes - Income Tax Provision Differences from Expected Statutory Provision (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Expected provision at statutory rate	21.00%	21.00%	35.00%
Difference resulting from:
Tax exempt interest income, net of disallowance	(3.20%)	(4.00%)	(6.10%)
Increase in value of bank owned life insurance assets	(0.80%)	(1.10%)	(2.20%)
Stock-based compensation	0.00%	(0.20%)	(1.00%)
State income taxes, net of federal benefits	0.40%	1.60%	1.20%
Adjustment to deferred tax assets and liabilities for enacted changes in tax laws and rates	0	(0.005)	0.017
Changes in valuation allowance	0.20%	0.10%	0.50%
Other	0.30%	(0.20%)	(0.40%)
Provision for income taxes - effective income tax rate	17.90%	16.70%	28.70%