Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Total fair value	$ 97,563	$ 98,562
Money market funds [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Fair Value Measurement	97,563	98,562
Quoted prices in active markets for identical assets (Level 1) [Member]
Fair value of financial assets measured on a recurring basis
Fair Value Measurement	3,000	2,000
Quoted prices in active markets for identical assets (Level 1) [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Total fair value	97,563	98,562
Quoted prices in active markets for identical assets (Level 1) [Member] | Money market funds [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Fair Value Measurement	97,563	98,562
Significant other observable inputs (Level 2) [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Total fair value
Significant other observable inputs (Level 2) [Member] | Money market funds [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Fair Value Measurement
Significant unobservable inputs (Level 3) [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Total fair value
Significant unobservable inputs (Level 3) [Member] | Money market funds [Member] | Fair value on a recurring basis [Member]
Fair value of financial assets measured on a recurring basis
Fair Value Measurement