Marketable Securities (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Gain (Loss) on Investments [Line Items]
Maximum maturity of debt securities (less than 5 years)	5 years
Net pre-tax unrealized losses	$ 54,000	$ 22,000
Proceeds from sales of marketable securities	545,000	0
Available-for-sale securities, gross realized gain (loss)	3,000	0
Marketable securities classified as cash equivalents	2,500,000	1,600,000
Unrealized gains or losses on marketable securities	$ 0	$ 0