Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

The following table summarizes the Company's financial assets and liabilities measured at fair value on a recurring basis at March 31, 2019 and December 31, 2018 by level within the fair value hierarchy. Financial assets and financial liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement (in thousands):

	As of  March 31, 2019
	Quoted		Significant
	Prices in		Other		Significant
	Active		Observable		Unobservable
	Markets		Inputs		Inputs		Total Fair
	(Level 1)		(Level 2)		(Level 3)		Value
	(in thousands)
Assets:
Cash equivalents:
Money market funds	$	218,495		—		—	$	218,495
U.S. treasury securities		—		—		—		—
U.S. government and agency securities		—		—		—		—
Short-term investments:
U.S. treasury securities		—		15,716		—		15,716
U.S. government and agency securities		—		7,239		—		7,239
Total financial assets	$	218,495	$	22,955	$	—	$	241,450
	As of December 31, 2018
	Quoted		Significant
	Prices in		Other		Significant
	Active		Observable		Unobservable
	Markets		Inputs		Inputs		Total Fair
	(Level 1)		(Level 2)		(Level 3)		Value
	(in thousands)
Assets:
Cash equivalents:
Money market funds	$	47,258		—		—	$	47,258
U.S. treasury securities		—		—		—		—
U.S. government and agency securities		—		2,272		—		2,272
Short-term investments:
U.S. treasury securities		—		38,809		—		38,809
U.S. government and agency securities		—		6,732		—		6,732
Total financial assets	$	47,258	$	47,813	$	—	$	95,071