Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Short-term Investments [Member]	Dec. 31, 2013 Marketable securities [Member]	Sep. 30, 2014 Marketable securities [Member]
Available-for-sale Securities
Cost					$ 49,559	$ 17,649	$ 9,678
Gross Unrealized Losses					(44)	(3,300)	(786)
Gross Unrealized Gains					5	172	270
Available-for-sale Securities, Estimated Fair Value					49,520	14,521	9,162
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Unrealized Losses Total					(44)	(3,300)	(786)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than twelve Months, Unrealized Losses					(44)		(107)
Less than twelve Months, Fair Value					33,125		1,904
Twelve months or more, Unrealized Losses					0		(679)
Twelve months or more, Fair Value					0		1,365
Unrealized Losses					(44)		(786)
Fair Value					33,125		3,269
Investment in Marketable Securities (Textual) [Abstract]
Unrealized gain (loss) on available for sale securities	(1,086)	301	(1,487)	(10,756)
Impairment of marketable securities	$ 1,092	$ 870	$ 4,614	$ 18,097