Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 investment	Mar. 31, 2012	Dec. 31, 2012
Investment in Marketable Securities (Textual) [Abstract]
Other comprehensive unrealized gain	$ (3,531)
Marketable Securities, Unrealized Gain (Loss)		424
Number of investments, unrealized loss position, not other than temporary impairment	7
Short term investments	1,498		999
Marketable securities [Member]
Available-for-sale Securities
Available-for-sale Securities, Amortized Cost	34,751		34,786
Available-for-sales Securities, Gross Unrealized Losses	(13,072)		(10,443)
Available-for-sale Securities, Gross Unrealized Gains	1,819		2,722
Available-for-sale Securities, Estimated Fair Value	$ 23,498		$ 27,065