Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets Measured on Recurring Basis

The following tables set 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 September 30, 2018
	Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	58,404	$	58,404	$	—	$	—
U.S. government agency obligations		89,461		—		89,461		—
Corporate securities and commercial paper		117,718		—		117,718		—
	$	265,583	$	58,404	$	207,179	$	—

	Fair Value Measurements at December 31, 2017
	Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	66,478	$	66,478	$	—	$	—
U.S. government agency obligations		57,153		—		57,153		—
Corporate securities and commercial paper		52,072		—		52,072		—
	$	175,703	$	66,478	$	109,225	$	—

Schedule of Investments Classified as Available for Sale Securities with Contractual Maturities

Classified as (with contractual maturities):

	September 30, 2018		December 31, 2017
Cash and Cash equivalents	$	74,889	$	98,426
Short-term investments (due within one year)		182,948		77,277
Long-term investments (due between one and two years)		7,746		—
	$	265,583	$	175,703

Schedule of Available for Sale Securities at Fair Value Measurements

	Fair Value Measurements at September 30, 2018
	Amortized Cost		Unrealized Gain		Unrealized Loss			Fair Value
Money market funds	$	58,404	$	—	$	—		$	58,404
U.S. government agency obligations		89,505				(43	)		89,462
Corporate securities and commercial paper		117,784		—		(67	)		117,717
	$	265,693	$	—	$	(110	)	$	265,583

	Fair Value Measurements at December 31, 2017
	Amortized Cost		Unrealized Gain		Unrealized Loss			Fair Value
Money market funds	$	66,478	$	—	$	—		$	66,478
U.S. government agency obligations		57,183		—		(30	)		57,153
Corporate securities and commercial paper		52,084		—		(12	)		52,072
	$	175,745	$	—	$	(42	)	$	175,703