Fair Value Measurements (Details) - Recurring basis - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets measured at fair value on a recurring basis:
Total assets at fair value	$ 66,116	$ 83,637
Money market deposits
Assets measured at fair value on a recurring basis:
Total assets at fair value	10,445	13,928
Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value	29,724	29,224
Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	7,022	22,359
Corporate equity securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	18,925	18,126
Actively Quoted Markets for Identical Assets Level 1
Assets measured at fair value on a recurring basis:
Total assets at fair value	10,445	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	10,445	13,928
Significant Other Observable Inputs Level 2
Assets measured at fair value on a recurring basis:
Total assets at fair value	55,671	69,709
Significant Other Observable Inputs Level 2 | Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value	29,724	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	7,022	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	$ 18,925	$ 18,126