Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

Financial assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 are classified in the table below in one of the three categories described above (in thousands):

	September 30, 2018
	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Assets At Fair Value
Assets:
Money market funds	$	26,353	$	—	$	—	$	26,353
U.S. Treasury securities		79,392		—		—		79,392
Agency bonds		—		27,666		—		27,666
Commercial paper		—		62,856		—		62,856
Corporate obligations		—		13,879		—		13,879
	$	105,745	$	104,401	$	—	$	210,146

	December 31, 2017
	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Assets At Fair Value
Assets:
Money market funds	$	51,001	$	—	$	—	$	51,001
U.S. Treasury securities		165,801		—		—		165,801
Agency bonds		—		54,329		—		54,329
Equity securities		573		—		—		573
	$	217,375	$	54,329	$	—	$	271,704