Investment Securities And Short-Term Investments (Narrative) (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) security	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Investments [Line Items]
Equity investment, impairment	$ 8,828,000
Loss on equity impairments	$ 2,715,000
Number of marketable equity security investments | security	1
Unrealized holding loss	$ 175,000	$ 194,000
Short-term investments, interest income	921,000	1,450,000
Unrealized losses	$ 2,328,000		$ 87,000
Unrealized loss as a percentage of amortized cost	2.30%
Tapout [Member]
Schedule of Investments [Line Items]
Equity investment, impairment	$ 0	$ 0