Income Taxes - Schedule of Income Tax Amounts were Recorded in Shareholder's Equity as Elements of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Securities and defined benefit pension plan unrecognized items	$ 9,730	$ 11,570	$ (1,250)