Cash and Cash Equivalents and Investments in Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Investment Income, Interest	$ 673	$ 1,004	$ 2,403	$ 3,593
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	$ 500		$ 1,400	$ 1,700