Cash and Cash Equivalents and Investments in Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Investment Income, Interest	$ 176	$ 527	$ 995	$ 602
Maximum term to maturity from date of purchase (years)	1 year
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Income, Interest	$ 100		$ 300	$ 100