Investments and Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of investments
Amortized Cost	$ 62,258	$ 73,262
Gross Unrealized Gains		26
Gross Unrealized (Losses)	(1)
Estimated Fair Value	62,257	73,288
Cash equivalents [Member]
Schedule of investments
Amortized Cost	8,184	18,836
Gross Unrealized Gains
Gross Unrealized (Losses)
Estimated Fair Value	8,184	18,836
Cash equivalents [Member] | Money market funds [Member]
Schedule of investments
Amortized Cost	8,184	15,839
Gross Unrealized Gains
Gross Unrealized (Losses)
Estimated Fair Value	8,184	15,839
Cash equivalents [Member] | U.S. government sponsored entity debt securities [Member]
Schedule of investments
Amortized Cost		2,997
Gross Unrealized Gains
Gross Unrealized (Losses)
Estimated Fair Value		2,997
Available-for-sale securities [Member]
Schedule of investments
Amortized Cost	54,074	54,426
Gross Unrealized Gains		26
Gross Unrealized (Losses)	(1)
Estimated Fair Value	54,073	54,452
Available-for-sale securities [Member] | U.S. government sponsored entity debt securities [Member]
Schedule of investments
Amortized Cost	54,074	54,426
Gross Unrealized Gains		26
Gross Unrealized (Losses)	(1)
Estimated Fair Value	$ 54,073	$ 54,452