Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 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 December 31, 2018
	Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	45,017	$	45,017	$	—	$	—
U.S. government agency obligations		103,940		—		103,940		—
Corporate securities and commercial paper		110,768		—		110,768		—
	$	259,725	$	45,017	$	214,708	$	—

	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):

	December 31, 2018		December 31, 2017
Cash and cash equivalents	$	71,064	$	98,426
Short-term investments (due within one year)		185,480		77,277
Long-term investments (due between one and two    years)		3,181		—
	$	259,725	$	175,703

Schedule of Available for Sale Securities at Fair Value Measurements

	Fair Value Measurements at December 31, 2018
	Amortized Cost		Unrealized Gain		Unrealized Loss			Fair Value
Money market funds	$	45,017	$	—	$	—		$	45,017
U.S. government agency obligations		103,957		—		(17	)		103,940
Corporate securities and commercial paper		110,859		—		(91	)		110,768
	$	259,833	$	—	$	(108	)	$	259,725

	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