Fair Value Measurements (Details) (Fair Value Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	$ 42,041	$ 39,040
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	8,047	52
Significant Other Observable Inputs (Level 2) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	33,994	38,988
Significant Unobservable Inputs (Level 3) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	0	0
U.S. Treasury securities [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	33,994	38,988
U.S. Treasury securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	0	0
U.S. Treasury securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	33,994	38,988
U.S. Treasury securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	0	0
Money market funds [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	8,047	52
Money market funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	8,047	52
Money market funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	0	0
Money market funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Schedule of financial instruments measured at fair value on a recurring basis
Total assets at fair value	$ 0	$ 0