Comprehensive Income/(Loss) - Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 3,781,579	$ 2,538,362	$ 2,790,281	$ 2,533,062
Amounts reclassified from accumulated other comprehensive income/(loss)	(364)	(126)	(579)	(237)
Total other comprehensive income (loss)	17,066	(286)	44,988	(8,515)
Ending Balance	3,819,220	2,544,279	3,819,220	2,544,279
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			5,124	6,515
Other comprehensive income (loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income/(loss)	(148)	(77)	(275)	(130)
Total other comprehensive income (loss)			(275)	(130)
Ending Balance	4,849	6,385	4,849	6,385
Accumulated Unrealized Gains (Losses) on Debt Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(223,756)	(233,208)
Other comprehensive income (loss) before reclassifications			45,567	(8,278)
Amounts reclassified from accumulated other comprehensive income/(loss)	(216)	(49)	(304)	(107)
Total other comprehensive income (loss)			45,263	(8,385)
Ending Balance	(178,493)	(241,593)	(178,493)	(241,593)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(190,710)	(234,922)	(218,632)	(226,693)
Other comprehensive income (loss) before reclassifications			45,567	(8,278)
Amounts reclassified from accumulated other comprehensive income/(loss)			(579)	(237)
Total other comprehensive income (loss)	17,066	(286)	44,988	(8,515)
Ending Balance	$ (173,644)	$ (235,208)	$ (173,644)	$ (235,208)