Income Taxes - Percentage of Pretax Earnings, Differs from Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
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	(3.00%)	(3.80%)	(4.40%)
Other	(0.20%)	1.00%	(0.10%)
Effective income tax rate	17.80%	18.20%	16.50%