Income Taxes - Income Tax Expense from Operations from the Amount Computed by Applying the U.S. Federal Income Tax Statutory Rate of 21% to Income Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	$ 16,684	$ 22,453	$ 24,258
Tax-exempt interest, net	(2,511)	(3,226)	(2,999)
State income tax	911	1,080	(591)
Dividends received deduction	(107)	(89)	(59)
Valuation allowance	(1,803)	46	2,025
Prior year adjustments	344	3	30
Other	175	50	163
Income tax expense, Total	$ 13,693	$ 20,317	$ 22,827