Fair Value Measurements (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Assets measured at fair value on a recurring basis:
Total assets at fair value	$ 66,911	$ 83,637
Money market deposits
Assets measured at fair value on a recurring basis:
Total assets at fair value	14,017	13,928
Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value	27,224	29,224
Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	13,014	22,359
Corporate equity securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	12,656	18,126
Actively Quoted Markets for Identical Assets Level 1
Assets measured at fair value on a recurring basis:
Total assets at fair value	14,017	13,928
Actively Quoted Markets for Identical Assets Level 1 | Money market deposits
Assets measured at fair value on a recurring basis:
Total assets at fair value	14,017	13,928
Significant Other Observable Inputs Level 2
Assets measured at fair value on a recurring basis:
Total assets at fair value	52,894	69,709
Significant Other Observable Inputs Level 2 | Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value	27,224	29,224
Significant Other Observable Inputs Level 2 | Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	13,014	22,359
Significant Other Observable Inputs Level 2 | Corporate equity securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	$ 12,656	$ 18,126