Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of short-term investments
Short-term Investments, Amortized Cost	$ 33,990	$ 38,980
Short-term Investments, Gross Unrealized Holding Gains	4	8
Short-term Investments, Gross Unrealized Holding Losses	0	0
Short-term Investments, Fair Value	33,994	38,988
U.S. Treasury securities [Member]
Schedule of short-term investments
Short-term Investments, Amortized Cost	33,990	38,980
Short-term Investments, Gross Unrealized Holding Gains	4	8
Short-term Investments, Gross Unrealized Holding Losses	0	0
Short-term Investments, Fair Value	$ 33,994	$ 38,988