Fair Value Measurements (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Jul. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Assets measured at fair value on a recurring basis:
Purchase of other investments		$ 6,100
Subordinated convertible promissory notes
Assets measured at fair value on a recurring basis:
Purchase of other investments	$ 6,100
Significant Unobservable Inputs Level 3 | Subordinated convertible promissory notes | Other assets
Assets measured at fair value on a recurring basis:
Estimated fair value		5,800
Recurring basis
Assets measured at fair value on a recurring basis:
Total assets at fair value		75,411	$ 83,637
Recurring basis | Money market deposits
Assets measured at fair value on a recurring basis:
Total assets at fair value		10,809	13,928
Recurring basis | Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value		34,717	29,224
Recurring basis | Corporate debt securities
Assets measured at fair value on a recurring basis:
Total assets at fair value		14,883	22,359
Recurring basis | Corporate equity securities
Assets measured at fair value on a recurring basis:
Total assets at fair value		15,002	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		10,809	13,928
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		10,809	13,928
Recurring basis | Significant Other Observable Inputs Level 2
Assets measured at fair value on a recurring basis:
Total assets at fair value		64,602	69,709
Recurring basis | Significant Other Observable Inputs Level 2 | Commercial paper
Assets measured at fair value on a recurring basis:
Total assets at fair value		34,717	29,224
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		14,883	22,359
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		$ 15,002	$ 18,126