Income Taxes - Reconciliation of Effective Tax Rate and Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%	35.00%
State income taxes, net of federal tax benefit	7.90%	8.60%	6.90%
Tax Cuts and Jobs Act impact of federal rate change	0.00%	0.00%	9.60%
Tax-exempt interest on municipal obligations	(0.70%)	(1.00%)	(1.90%)
Tax-exempt life insurance related income	(0.60%)	(0.60%)	(1.30%)
Low income housing tax credits	(2.30%)	(2.20%)	(2.30%)
Low income housing tax credit amortization	2.10%	2.00%	2.10%
Equity compensation	(0.40%)	(0.40%)	(1.10%)
Non-deductible merger expenses	0.00%	0.20%	0.20%
Other	0.40%	(0.80%)	0.50%
Effective Tax Rate	27.40%	26.80%	47.70%