Cash and Cash Equivalents and Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents
Fair Value
Amortized Cost	$ 46,517	$ 37,499
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	46,517	37,499
Certificates of Deposit
Fair Value
Amortized Cost	552	552
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	552	552
U.S. Treasury Securities
Fair Value
Amortized Cost	51,288	91,075
Gross Unrealized Gains	10	3
Gross Unrealized Losses	0	(1)
Estimated Fair Value	51,298	91,077
Total Short-term Investments
Fair Value
Amortized Cost	51,840	91,627
Gross Unrealized Gains	10	3
Gross Unrealized Losses	0	(1)
Estimated Fair Value	51,850	91,629
Total Cash and Cash Equivalents and Investments
Fair Value
Amortized Cost	98,357	129,126
Gross Unrealized Gains	10	3
Gross Unrealized Losses	0	(1)
Estimated Fair Value	$ 98,367	$ 129,128