Investment Securities - Investments in Debt and Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Cost
Equity	$ 350,947	$ 344,669
Debt	903,715	908,316
Other	7,549	2,889
Total	1,262,211	1,255,874
Gains
Equity	292,940	246,795
Debt	2,574	3,938
Other	1	61
Total	295,515	250,794
Losses
Equity	(6,033)	(5,549)
Debt	(27,229)	(25,181)
Other	(10)	(36)
Total	(33,272)	(30,766)
Fair Value
Equity	637,854	585,915
Debt	879,060	887,073
Other	7,540	2,914
Total	$ 1,524,454	$ 1,475,902