Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Disclosures [Abstract]

Summary of Fair Value Assets and Liabilities Measured on Recurring Basis

The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands):

	Fair Value Measurements at March 31, 2018
	Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	183,714	$	183,714	$	—	$	—
U.S. government agency obligations		23,875		—		23,875		—
Corporate securities		51,568		—		51,568		—
Total	$	259,157	$	183,714	$	75,443	$	—
	Fair Value Measurements at December 31, 2017
	Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	223,568	$	223,568	$	—	$	—
U.S. government agency obligations		27,878		—		27,878		—
Corporate securities		23,955		—		23,955		—
Total	$	275,401	$	223,568	$	51,833	$	—

Summary of Fair Value Measurement of Available-for-sale Securities

The following table is a summary of amortized cost, unrealized gain and loss, and fair value of the Company’s marketable securities by contractual maturities (in thousands):

	Fair Value Measurements at March 31, 2018
	Amortized Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash equivalents (due within 90 days)	$	183,714	$	—	$	—		$	183,714
Short-term investments (due within one year)		39,998		—		(176	)	$	39,822
Long-term investments (due between one and two years)		35,769		—		(148	)	$	35,621
Total	$	259,481	$	—	$	(324	)	$	259,157
	FairValue Measurements at December 31, 2017
	Amortized Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash equivalents (due within 90 days)	$	223,568	$	—	$	—		$	223,568
Short-term investments (due within one year)		32,010		—		(77	)		31,933
Long-term investments (due between one and two years)		20,010		—		(110	)		19,900
Total	$	275,588	$	—	$	(187	)	$	275,401