Investments Gain (Loss) on Marketable Equity Securities) (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments [Abstract]
Gain (loss) on marketable equity securities, net	$ 61,926	$ 59,364	$ 39,890	$ (100,393)	$ 49,407	$ 17,404	$ 7,791	$ 24,066	$ 60,787	$ 98,668	$ (15,843)
Less: Net (gains) losses in earnings from marketable equity securities sold									13,382	(2,810)	4,271
Net unrealized gains (losses) in earnings from marketable equity securities still held at the end of the year									$ 74,169	$ 95,858	$ (11,572)