Income Taxes - Reconciliation from Federal Statutory Income Tax Rate to Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%	35.00%
Tax reform remeasurement	0.00%	0.00%	8.60%
Net tax-exempt interest income on securities and loans of state and political subdivisions	(3.30%)	(3.20%)	(6.00%)
State income taxes, net of federal tax effect	1.70%	1.70%	1.30%
Bank-owned life insurance	(0.60%)	(0.80%)	(1.10%)
General business credits	(2.20%)	(1.60%)	(1.70%)
All other—net	1.20%	0.90%	0.20%
Effective tax rate	17.80%	18.00%	36.30%