Fair Value of Financial Instruments (Details) (Fair Value Measurements Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Cash equivalents:
Total cash equivalents		$ 6,950
Short-term investments:
Total short-term investments		42,882
Cash equivalents and short-term investments		49,832
Money market mutual funds [Member]
Cash equivalents:
Total cash equivalents	50,432	4,201
Commercial paper [Member]
Cash equivalents:
Total cash equivalents		2,749
Certificate of deposit [Member]
Short-term investments:
Total short-term investments		746
Municipal securities [Member]
Short-term investments:
Total short-term investments		33,592
Commercial paper [Member]
Short-term investments:
Total short-term investments		3,645
Corporate bonds [Member]
Short-term investments:
Total short-term investments		4,899
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Cash equivalents:
Total cash equivalents		4,201
Short-term investments:
Cash equivalents and short-term investments		4,201
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market mutual funds [Member]
Cash equivalents:
Total cash equivalents	50,432	4,201
Significant Other Observable Inputs (Level 2) [Member]
Cash equivalents:
Total cash equivalents		2,749
Short-term investments:
Total short-term investments		42,882
Cash equivalents and short-term investments		45,631
Significant Other Observable Inputs (Level 2) [Member] | Money market mutual funds [Member]
Cash equivalents:
Total cash equivalents
Significant Other Observable Inputs (Level 2) [Member] | Commercial paper [Member]
Cash equivalents:
Total cash equivalents		2,749
Significant Other Observable Inputs (Level 2) [Member] | Certificate of deposit [Member]
Short-term investments:
Total short-term investments		746
Significant Other Observable Inputs (Level 2) [Member] | Municipal securities [Member]
Short-term investments:
Total short-term investments		33,592
Significant Other Observable Inputs (Level 2) [Member] | Commercial paper [Member]
Short-term investments:
Total short-term investments		3,645
Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Short-term investments:
Total short-term investments		4,899
Significant Unobservable Inputs (Level 3) [Member]
Cash equivalents:
Total cash equivalents
Short-term investments:
Total short-term investments
Cash equivalents and short-term investments
Significant Unobservable Inputs (Level 3) [Member] | Money market mutual funds [Member]
Cash equivalents:
Total cash equivalents