Available-for-Sale Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2019

Investments Debt And Equity Securities [Abstract]

Summary of Available-for-Sale Marketable Securities by Major Type of Security

The following tables summarize the Company's available-for-sale marketable securities by major type of security as of March 31, 2019 and December 31, 2018:

As of March 31, 2019

			Gross Unrealized
Type of Security	Amortized Cost		Gains		Losses			Estimated Fair Value
U.S. Treasury securities	$	15,921	$	16	$	—		$	15,937
U.S. government agency obligations		12,440		7		—			12,447
Corporate bonds		69,914		56		(10	)		69,960
Commercial paper		38,104		6		(2	)		38,108
Municipal bonds		5,500		—		—			5,500
Total available-for-sale marketable securities	$	141,879	$	85	$	(12	)	$	141,952

As of December 31, 2018

			Gross Unrealized
Type of Security	Amortized Cost		Gains		Losses			Estimated Fair Value
U.S. Treasury securities	$	19,540	$	—	$	(1	)	$	19,539
U.S. government agency obligations		17,860		—		(1	)		17,859
Corporate bonds		75,999		5		(94	)		75,910
Commercial paper		50,413		—		(23	)		50,390
Municipal bonds		4,000		—		—			4,000
Total available-for-sale marketable securities	$	167,812	$	5	$	(119	)	$	167,698

Schedule of Amortized Cost and Fair Values of Marketable Debt Securities by Contractual Maturity

The Company classifies its marketable debt securities based on their contractual maturity dates.As of March 31, 2019, the Company’s marketable debt securities mature at various dates through March 2021. The amortized cost and fair values of marketable debt securities by contractual maturity were as follows.

	As of March 31, 2019				As of December 31, 2018
Contractual maturity	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than one year	$	120,201	$	120,265	$	146,363		146,302
One year to two years		21,678		21,687		21,449		21,396
Total	$	141,879	$	141,952	$	167,812	$	167,698

Schedule of Fair Values and Continuous Unrealized Loss Positions of Available-for-Sale Marketable Securities

The following tables show the fair value of the Company's available-for-sale marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual investments have been in a continuous unrealized loss position.

As of March 31, 2019

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Corporate bonds	$	14,761	$	(10	)	$	—	$	—	$	14,761	$	(10	)
Commercial paper		15,884		(2	)		—		—		15,884		(2	)
Total	$	30,645	$	(12	)	$	—	$	—	$	30,645	$	(12	)

As of December 31, 2018

	Less than 12 Months					12 Months or Greater				Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
U.S. Treasury securities	$	16,392	$	(1	)	$	—	$	—	$	16,392	$	(1	)
U.S. government agency obligations		5,596		(1	)		—		—		5,596		(1	)
Corporate bonds		71,322		(94	)		—		—		71,322		(94	)
Commercial paper		39,445		(23	)		—		—		39,445		(23	)
Total	$	132,755	$	(119	)	$	—	$	—	$	132,755	$	(119	)