Fair Values of Assets and Liabilities (Summary of Assets Measured at Fair Value on a Nonrecurring Basis) (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	$ 109,011	$ 109,011	$ 183,667
Fair value losses - individually assessed loans - foreclosure probable and collateral-dependent	1,425	17,956
Fair value losses - other real estate owned	93	1,012
Fair value losses	1,518	18,968
Measured at fair value on a non-recurring basis:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	78,653	78,653
Other real estate owned	13,845	13,845
Total financial assets	92,498	92,498
Measured at fair value on a non-recurring basis: | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	0	0
Other real estate owned	0	0
Total financial assets	0	0
Measured at fair value on a non-recurring basis: | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	0	0
Other real estate owned	0	0
Total financial assets	0	0
Measured at fair value on a non-recurring basis: | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually assessed loans - foreclosure probable and collateral-dependent	78,653	78,653
Other real estate owned	13,845	13,845
Total financial assets	$ 92,498	$ 92,498