Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income, Net of Tax) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 512,970
Net other comprehensive income (loss) during period	(165,652)	$ 245,600	$ 330,970
Ending Balance	347,318	512,970
Available-for-sale Securities [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	563,801	313,304	(16,103)
Other comprehensive income (loss) before reclassification	(183,537)	336,598	329,638
Reclassification of amounts included in net income	(55)	(86,101)	(231)
Net other comprehensive income (loss) during period	(183,592)	250,497	329,407
Ending Balance	380,209	563,801	313,304
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(50,831)	(45,934)	(47,497)
Other comprehensive income (loss) before reclassification	13,108	(9,099)	(2,879)
Reclassification of amounts included in net income	4,832	4,202	4,442
Net other comprehensive income (loss) during period	17,940	(4,897)	1,563
Ending Balance	(32,891)	(50,831)	(45,934)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	512,970	267,370	(63,600)
Other comprehensive income (loss) before reclassification	(170,429)	327,499	326,759
Reclassification of amounts included in net income	4,777	(81,899)	4,211
Net other comprehensive income (loss) during period	(165,652)	245,600	330,970
Ending Balance	$ 347,318	$ 512,970	$ 267,370