Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Investments
Amortized Cost	$ 58,574		$ 58,574		$ 76,019
Gross Unrealized Gains	(5)		(5)		3
Gross Unrealized Losses	5		5
Fair Value	58,574		58,574		76,022
Realized gains or losses recorded from the sale of marketable securities	0	0	0	0
Cash And Cash Equivalent [Member]
Investments
Fair Value	8,443		8,443		53,306
Marketable Securities [Member]
Investments
Fair Value					22,511
Marketable Securities Current [Member]
Investments
Fair Value	48,981		48,981
Marketable Securities Non Current [Member]
Investments
Fair Value	752		752
Restricted Cash [Member]
Investments
Fair Value	398		398		205
Money Market Funds [Member]
Investments
Amortized Cost	8,840		8,840		53,511
Fair Value	8,840		8,840		53,511
U S Government Corporations And Agencies Securities [Member]
Investments
Amortized Cost	15,099		15,099		12,301
Gross Unrealized Gains	(5)		(5)
Fair Value	15,094		15,094		12,301
Commercial Paper [Member]
Investments
Amortized Cost	10,244		10,244		8,246
Gross Unrealized Gains					3
Gross Unrealized Losses	5		5
Fair Value	10,249		10,249		8,249
Corporate Debt Securities [Member]
Investments
Amortized Cost	24,391		24,391		1,961
Fair Value	$ 24,391		$ 24,391		$ 1,961