Fair Value of Financial Assets and Liability

9 Months Ended

Sep. 30, 2018

Fair Value of Financial Assets and Liability

Fair Value of Financial Assets and Liability

4. Fair Value of Financial Assets and Liability

As of September 30, 2018 and December 31, 2017, the carrying amount of cash and cash equivalents and short‑term investments was $272,386 and $148,082, respectively, which approximates fair value. Cash and cash equivalents and short‑term investments includes investments in money market funds that invest in U.S. government securities that are valued using quoted market prices. Accordingly, money market funds and government funds are categorized as Level 1 and had a total balance of $57,856 and $34,698 as of September 30, 2018 and December 31, 2017, respectively.  The financial assets valued based on level 2 inputs consist of corporate debt securities and commercial paper, which consist of investments in highly-rated investment-grade corporations.

A financial liability was recognized by the Company during the nine months ended September 30, 2017 related to the 2017 Series A Investor Instrument. The liability was valued based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. Upon the closing of the second tranche of the 2017 Series A preferred financing in August 2017, this liability was settled.

The following tables present information about the Company's financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:

	Fair value Measurements as of
	September 30, 2018 using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash Equivalents:
Corporate Debt Securities and Commercial Paper	$	—	$	—	$	—	$	—
Money Market Funds		57,856		—		—		57,856
Marketable Securities:
Corporate Debt Securities and Commercial Paper		—		214,139		—		214,139
U.S. Treasury Securities		—		—		—		—
Total	$	57,856	$	214,139	$	—	$	271,995

	Fair value Measurements as of
	December 31, 2017 using:
	Level 1		Level 2		Level 3		Total
Assets:
Cash Equivalents:
Corporate Debt Securities	$	—	$	15,104	$	—	$	15,104
Money Market Funds		17,753		—		—		17,753
Marketable Securities:
Corporate Debt Securities		—		96,901		—		96,901
U.S. Treasury Securities		16,945		—		—		16,945
Total	$	34,698	$	112,005	$	—	$	146,703

Marketable Securities

The following tables summarize the Company's marketable securities:

	September 30, 2018
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Assets
Corporate Debt Securities and Commercial Paper (due within 1 year)	$	214,225	$	4	$	(90)	$	214,139
U.S. Treasury Securities (due within 1 year)		—		—		—		—
	$	214,225	$	4	$	(90)	$	214,139

	December 31, 2017
			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Assets
Corporate Debt Securities (due within 1 year)	$	97,029	$	—	$	(128)	$	96,901
U.S. Treasury Securities (due within 1 year)		16,958		—		(13)		16,945
	$	113,987	$	—	$	(141)	$	113,846

Below is a roll forward of the fair value of the 2017 Series A Investor Instrument for the nine months ended September 30, 2017:

	2017 Series A Investor
	Instrument
Fair value at December 31, 2016	$	—
Fair value upon the January 2017 Initial Closing, net		328
Change in fair value		1,863
Reclassification of liability upon August 2017 Second Tranche Closing		(2,191)
Fair value at September 30, 2017	$	—

The fair value of the Series A Investor Instrument is the sum of the probability‑weighted fair value of the 2017 Investor Right/Obligation and the 2017 Series A Call Option.

The following assumptions and inputs were used in determining the fair value of the 2017 Series A Investor Call Option valued using the Black‑ Scholes option pricing model:

	August 2017 Second Tranche Closing
Series A Convertible Preferred Stock Exercise Price	$	1.00
Series A Convertible Preferred Stock Fair Value	$	1.33
Expected term		1.5 months
Expected volatility		64.0	%
Expected interest rate		0.95	%
Expected dividend yield		—

In August 2017, upon the closing of the second tranche of the series A preferred stock financing, the 2017 Series A Investor Call Option expired unexercised.

The Company estimated the fair value of the 2017 Series A Investor Right/Obligation as the probability‑weighted present value of the expected benefit of the investment. The expected benefit is the difference between the expected future value of shares issued upon the second tranche closing and the investment price for the second tranche closing. The expected future value is estimated as a weighted average of IPO and remain private scenarios, and the future value is converted to a present value assuming a closing date of October 15, 2017 and a nominal, risk‑free discount rate.