Investment Securities And Short-Term Investments (Narrative) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) security	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Investments [Line Items]
Equity investment, impairment			$ 8,828,000
Loss on equity impairments		$ 0	$ 2,715,000	$ 0
Number of nonmarketable equty investments, involved in merger | security	1
Number of marketable equity security investments | security			2
Unrealized holding gain (loss)	$ 7,945,000	(3,597,000)	$ 7,770,000	(3,791,000)
Short-term investments, interest income	493,000	$ 1,343,000	1,414,000	2,793,000
Unrealized losses	$ 58,000		$ 58,000		$ 87,000
Unrealized loss as a percentage of amortized cost			1.00%
Tapout [Member]
Schedule of Investments [Line Items]
Equity investment, impairment				$ 0