Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period			$ (677,088)
Net comprehensive loss	$ (153,491)	$ (225,574)	(138,801)	$ (695,312)
Balance at the end of the period	(815,889)		(815,889)
Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(673)	57	(673)	57
Balance at the end of the period	(673)	57	(673)	57
Unrealized Gains and (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(661,725)	(490,941)	(676,415)	(21,203)
Other comprehensive loss before reclassifications	(153,491)	(225,551)	(138,768)	(695,289)
Amounts reclassified from accumulated other comprehensive loss		(23)	(33)	(23)
Net comprehensive loss	(153,491)	(225,574)	(138,801)	(695,312)
Balance at the end of the period	(815,216)	(716,515)	(815,216)	(716,515)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(662,398)	(490,884)	(677,088)	(21,146)
Other comprehensive loss before reclassifications	(153,491)	(225,551)	(138,768)	(695,289)
Amounts reclassified from accumulated other comprehensive loss		(23)	(33)	(23)
Net comprehensive loss	(153,491)	(225,574)	(138,801)	(695,312)
Balance at the end of the period	$ (815,889)	$ (716,458)	$ (815,889)	$ (716,458)