Comprehensive Income/(Loss) - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 2,426,662	$ 2,693,166	$ 2,756,737
Other comprehensive income/(loss) before reclassifications	35,238	(257,527)
Amounts reclassified from accumulated other comprehensive income/(loss)	485	231	1,869
Total other comprehensive gain (loss)	35,723	(257,296)	(36,479)
Ending Balance	2,533,062	2,426,662	2,693,166
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(535)	(398)	(15,502)
Other comprehensive income/(loss) before reclassifications	6,748	(358)	13,192
Amounts reclassified from accumulated other comprehensive income/(loss)	302	221	1,912
Total other comprehensive gain (loss)	7,050	(137)	15,104
Ending Balance	6,515	(535)	(398)
Accumulated Unrealized Gains (Losses) on Debt Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(261,881)	(4,722)	46,861
Other comprehensive income/(loss) before reclassifications	28,490	(257,169)	(51,540)
Amounts reclassified from accumulated other comprehensive income/(loss)	183	10	(43)
Total other comprehensive gain (loss)	28,673	(257,159)	(51,583)
Ending Balance	(233,208)	(261,881)	(4,722)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(262,416)	(5,120)	31,359
Other comprehensive income/(loss) before reclassifications			(38,348)
Amounts reclassified from accumulated other comprehensive income/(loss)			1,869
Total other comprehensive gain (loss)	35,723	(257,296)	(36,479)
Ending Balance	$ (226,693)	$ (262,416)	$ (5,120)