Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive (Loss) Income
Balance at the beginning of the period			$ (582,536)
Net comprehensive income (loss)	$ 140,571	$ (153,491)	102,896	$ (138,801)
Balance at the end of the period	(479,640)		(479,640)
Benefit Plans
Accumulated Other Comprehensive (Loss) Income
Balance at the beginning of the period	627	(673)	627	(673)
Balance at the end of the period	627	(673)	627	(673)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive (Loss) Income
Balance at the beginning of the period	(620,838)	(661,725)	(583,163)	(676,415)
Other comprehensive income (loss) before reclassifications	140,571	(153,491)	102,896	(138,768)
Amounts reclassified from accumulated other comprehensive loss				(33)
Net comprehensive income (loss)	140,571	(153,491)	102,896	(138,801)
Balance at the end of the period	(480,267)	(815,216)	(480,267)	(815,216)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive (Loss) Income
Balance at the beginning of the period	(620,211)	(662,398)	(582,536)	(677,088)
Other comprehensive income (loss) before reclassifications	140,571	(153,491)	102,896	(138,768)
Amounts reclassified from accumulated other comprehensive loss				(33)
Net comprehensive income (loss)	140,571	(153,491)	102,896	(138,801)
Balance at the end of the period	$ (479,640)	$ (815,889)	$ (479,640)	$ (815,889)