Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 3,783,977	$ 3,110,661
Other comprehensive (loss) income before reclassifications	(48,817)	64,418
Reclassification adjustment for net losses on AFS securities included in net income	0	0
Current period other comprehensive (loss) income, before tax	(48,817)	64,418
Income tax benefit (expense)	11,638	(15,358)
Total other comprehensive (loss) income	(37,179)	49,060
Ending balance	3,798,326	3,243,627
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(16,872)	(139,925)
Total other comprehensive (loss) income	(37,179)	49,060
Ending balance	(54,051)	(90,865)
Unrealized gains/losses on AFS securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(36,108)	(145,589)
Other comprehensive (loss) income before reclassifications	(50,155)	59,931
Reclassification adjustment for net losses on AFS securities included in net income	0	0
Current period other comprehensive (loss) income, before tax	(50,155)	59,931
Income tax benefit (expense)	11,957	(14,288)
Total other comprehensive (loss) income	(38,198)	45,643
Ending balance	(74,306)	(99,946)
Pension plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	19,236	5,664
Other comprehensive (loss) income before reclassifications	1,338	4,487
Reclassification adjustment for net losses on AFS securities included in net income	0	0
Current period other comprehensive (loss) income, before tax	1,338	4,487
Income tax benefit (expense)	(319)	(1,070)
Total other comprehensive (loss) income	1,019	3,417
Ending balance	$ 20,255	$ 9,081