Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Short-term Investments [Member]	Dec. 31, 2013 Marketable securities [Member]	Jun. 30, 2014 Marketable securities [Member]
Available-for-sale Securities
Cost					$ 47,661	$ 17,649	$ 13,972
Gross Unrealized Losses					(31)	(3,300)	(677)
Gross Unrealized Gains					12	172	466
Available-for-sale Securities, Estimated Fair Value					47,642	14,521	13,761
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Unrealized Losses Total					(31)	(3,300)	(677)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than twelve Months, Unrealized Losses					(31)		0
Less than twelve Months, Fair Value					29,090		0
Twelve months or more, Unrealized Losses					0		(677)
Twelve months or more, Fair Value					0		1,399
Unrealized Losses					(31)		(677)
Fair Value					29,090		1,399
Investment in Marketable Securities (Textual) [Abstract]
Unrealized gain (loss) on available for sale securities	(773)	(7,491)	(401)	(11,057)
Impairment of marketable securities	$ 934	$ 17,192	$ 3,522	$ 17,227