Available-for-Sale Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

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 December 31, 2017, and 2016:

As of December 31, 2017

			Gross Unrealized					Estimated Fair
Type of Security	Amortized Cost		Gains		Losses			Value
Money market funds	$	39,988	$	—	$	(37	)	$	39,951
U.S. government agency obligations		7,799		—		(5	)		7,794
Corporate bonds		15,919		—		(12	)		15,907
Commercial paper		19,545		—		(16	)		19,529
Total available-for-sale marketable securities	$	83,251	$	—	$	(70	)	$	83,181

As of December 31, 2016

			Gross Unrealized					Estimated Fair
Type of Security	Amortized Cost		Gains		Losses			Value
Money market funds	$	8,268	$	8	$	—		$	8,276
U.S. Treasury securities		2,523		—		(1	)		2,522
U.S. government agency obligations		3,501		1		—			3,502
Corporate bonds		16,683		—		(6	)		16,677
Commercial paper		15,206		3		(2	)		15,207
Total available-for-sale marketable securities	$	46,181	$	12	$	(9	)	$	46,184

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 December 31, 2017, the Company’s marketable debt securities mature at various dates through July 2018. The amortized cost and fair values of marketable debt securities by contractual maturity were as follows. The table does not include money market funds that are classified as available-for sale marketable securities.

	As of December 31,
	2017				2016
Contractual maturity	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than one year	$	43,263	$	43,230	$	37,913	$	37,908

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.

	Less than 12 Months					12 Months or Greater				Total
			Gross					Gross				Gross
			Unrealized					Unrealized				Unrealized
As of December 31, 2017	Fair Value		Losses			Fair Value		Losses		Fair Value		Losses
Money market funds	$	39,951	$	(37	)	$	—	$	—	$	39,951	$	(37	)
U.S. government agency obligations		7,794		(5	)		—		—		7,794		(5	)
Corporate bonds		15,907		(12	)		—		—		15,907		(12	)
Commercial paper		19,031		(16	)		—		—		19,031		(16	)
Total	$	82,683	$	(70	)	$	—	$	—	$	82,683	$	(70	)

	Less than 12 Months					12 Months or Greater				Total
			Gross					Gross				Gross
			Unrealized					Unrealized				Unrealized
As of December 31, 2016	Fair Value		Losses			Fair Value		Losses		Fair Value		Losses
U.S. Treasury securities	$	2,522	$	(1	)	$	—	$	—	$	2,522	$	(1	)
Corporate bonds		9,919		(6	)		—		—		9,919		(6	)
Commercial paper		5,227		(2	)		—		—		5,227		(2	)
Total	$	17,668	$	(9	)	$	—	$	—	$	17,668	$	(9	)