Securities (Net Gains and Losses on Trading Account Securities) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 1,014	$ 1,102	$ 2,173
Net mark-to-market gains (losses)	(75)	85	(176)
Net gain on trading account securities	$ 939	$ 1,187	$ 1,997