Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Changes in AOCI by component
Beginning balance	$ 6,784,943	$ 6,774,387	$ 6,835,917	$ 6,433,892
Ending balance	6,683,797	6,821,185	6,683,797	6,821,185
Cumulative Unrealized Gain (Loss) on Available-for- Sale Securities
Changes in AOCI by component
Beginning balance	17,355	28,970	20,955	40,953
OCI before reclassifications	(3,286)	(6,194)	45	(18,177)
Amounts reclassified from AOCI	45	0	(6,886)	0
Net period OCI	(3,241)	(6,194)	(6,841)	(18,177)
Ending balance	$ 14,114	$ 22,776	$ 14,114	$ 22,776