Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 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 June 30, 2018
	Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	348,525	$	348,525	$	—	$	—
U.S. government agency obligations		23,819		—		23,819		—
Corporate securities		55,595		—		55,595		—
Total	$	427,939	$	348,525	$	79,414	$	—
	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 June 30, 2018
	Amortized Cost		Unrealized Gain		Unrealized Loss			Fair Value
Cash equivalents (due within 90 days)	$	348,525	$	—	$	—		$	348,525
Short-term investments (due within one year)		51,576		—		(190	)		51,766
Long-term investments (due between one and two years)		27,584		—		(64	)		27,648
Total	$	427,685	$	—	$	(254	)	$	427,939
	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