Investments Marketable Equity Securities Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Marketable Equity Securities Gains (Losses) [Abstract]
Marketable equity securities gains (losses), net	$ 16,011	$ (51,408)
Less net gains recognized on marketable equity securities sold	263	323
Unrealized gains (losses) recognized on marketable equity securities held	$ 15,748	$ (51,731)