Fair Value Measurements (Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Equity securities, beginning of period		$ 168,809	$ 191,203
Purchases		28,900	56,250
Sales		(35,335)	(26,674)
Total gains (losses) included in net income (loss)	[1]	(108,646)	(51,970)
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Equity securities, end of period		$ 53,728	$ 168,809

[1] Included in change in fair value of equity securities in the consolidated statements of income (loss) and comprehensive income (loss) for the years ended December 31, 2018 and 2017.