Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets measured at fair value on a recurring basis:
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
Recurring basis
Assets measured at fair value on a recurring basis:
Total assets at fair value	83,637	88,581
Recurring basis | Money market deposits
Assets measured at fair value on a recurring basis:
Total assets at fair value	13,928	12,397
Recurring basis | Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value	29,224	29,749
Recurring basis | Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	22,359	46,435
Recurring basis | Corporate equity securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	18,126
Recurring basis | Actively Quoted Markets for Identical Assets Level 1
Assets measured at fair value on a recurring basis:
Total assets at fair value	13,928	12,397
Recurring basis | 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	13,928	12,397
Recurring basis | Significant Other Observable Inputs Level 2
Assets measured at fair value on a recurring basis:
Total assets at fair value	69,709	76,184
Recurring basis | Significant Other Observable Inputs Level 2 | Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value	29,224	29,749
Recurring basis | Significant Other Observable Inputs Level 2 | Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	22,359	$ 46,435
Recurring basis | Significant Other Observable Inputs Level 2 | Corporate equity securities
Assets measured at fair value on a recurring basis:
Total assets at fair value	$ 18,126