Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Recurring basis Actively Quoted Markets for Identical Assets Level 1	Dec. 31, 2013 Recurring basis Actively Quoted Markets for Identical Assets Level 1	Jun. 30, 2014 Recurring basis Actively Quoted Markets for Identical Assets Level 1 Money market deposits	Dec. 31, 2013 Recurring basis Actively Quoted Markets for Identical Assets Level 1 Money market deposits	Jun. 30, 2014 Recurring basis Significant Other Observable Inputs Level 2	Dec. 31, 2013 Recurring basis Significant Other Observable Inputs Level 2	Jun. 30, 2014 Recurring basis Significant Other Observable Inputs Level 2 Commercial paper	Dec. 31, 2013 Recurring basis Significant Other Observable Inputs Level 2 Commercial paper	Jun. 30, 2014 Recurring basis Significant Other Observable Inputs Level 2 Corporate debt securities	Dec. 31, 2013 Recurring basis Significant Other Observable Inputs Level 2 Corporate debt securities	Jun. 30, 2014 Recurring basis Fair value	Dec. 31, 2013 Recurring basis Fair value	Jun. 30, 2014 Recurring basis Fair value Money market deposits	Dec. 31, 2013 Recurring basis Fair value Money market deposits	Jun. 30, 2014 Recurring basis Fair value Commercial paper	Dec. 31, 2013 Recurring basis Fair value Commercial paper	Jun. 30, 2014 Recurring basis Fair value Corporate debt securities	Dec. 31, 2013 Recurring basis Fair value Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value			$ 15,368	$ 15,690	$ 15,368	$ 15,690	$ 73,209	$ 73,071	$ 25,746	$ 37,643	$ 47,463	$ 35,428	$ 88,577	$ 88,761	$ 15,368	$ 15,690	$ 25,746	$ 37,643	$ 47,463	$ 35,428
Transfer of assets from level 1 to level 2	0	0
Transfer of assets from level 2 to level 1	0	0
Transfer of liabilities from level 1 to level 2	0	0
Transfer of liabilities from level 2 to level 1	$ 0	$ 0