Cash and Cash Equivalents and Investments in Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Investment Income, Interest	$ 768	$ 1,184	$ 1,730	$ 2,589
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	$ 600	$ 900	$ 1,200