Income Taxes - Percentage of Pretax Earnings, Differs from Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	21.00%	21.00%
Reductions in tax rate resulting from interest income exempt from federal income tax	(4.40%)	(4.70%)	(4.60%)
Other	(0.10%)	0.00%	0.20%
Effective income tax rate	16.50%	16.30%	16.60%