Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	$ 3,004		$ 119,308
Gross, Unrealized Holding Gains	0		94
Gross, Unrealized Holding Losses	(3)		(11)
Fair Value	3,001	[1]	119,391	[2]
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	3,004		86,769
Gross, Unrealized Holding Gains	0		82
Gross, Unrealized Holding Losses	(3)		(11)
Fair Value	3,001	[1]	86,840	[2]
Commercial Paper [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost			30,482
Gross, Unrealized Holding Gains			8
Gross, Unrealized Holding Losses			0
Fair Value			30,490	[2]
Us Government Agencies Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost			2,057
Gross, Unrealized Holding Gains			4
Gross, Unrealized Holding Losses			0
Fair Value			$ 2,061	[2]

[1] Included in current marketable securities at June 30, 2013.

[2] Included in current marketable securities at December 31, 2012.