Investment Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Cost
Equity	$ 257,064	$ 262,564
Debt	668,068	613,271
Other	21,775	11,431
Total	946,907	887,266
Gains
Equity	229,874	219,658
Debt	8,379	18,090
Other	0	0
Total	238,253	237,748
Losses
Equity	(5,207)	(8,127)
Debt	(5,512)	(641)
Other	(32)	0
Total	(10,751)	(8,768)
Fair Value
Equity	481,731	474,095
Debt	670,935	630,720
Other	21,743	11,431
Total	$ 1,174,409	$ 1,116,246