Warrants (Tables)

12 Months Ended

Dec. 31, 2018

Other Liabilities Disclosure [Abstract]

Schedule of Warrants Issued and Outstanding

Warrants issued and outstanding at December 31, 2018 are as follows(in thousands, except share and per share data):

	Date			Number of Shares Underlying Warrants	Price per Share	Fair Value
Warrants to purchase	Issuance	Expiration
Common stock	3/1/2017	3/1/2027	[a]	1,388	5.94	$	5	[b]
Common stock	7/19/2013	7/22/2023	[a]	32,983	9.10	$	122	[b]
Common stock	11/26/2014	11/26/2024	[a]	6,680	16.47	$	49	[b]
Common stock	10/20/2015	10/20/2025	[a]	41,650	16.47	$	396	[c]
Common stock	11/9/2015	11/9/2025	[a]	25,709	16.47	$	244	[c]
Common stock	12/22/2016	12/22/2026	[a]	9,712	10.03	$	45	[c]
Total outstanding common stock warrants				118,122

[a] Common stock warrants will remain outstanding until exercised by the holder.

[b] Fair value at the date of issuance.

[c] Fair value at the date of conversion from redeemable convertible preferred stock to common stock warrants in conjunction with the IPO on October 16, 2018.    

Warrants issued and outstanding at December 31, 2017 are as follows (in thousands, except share and per share data):

	Series	Date			Number of Shares Underlying Warrants	Price per Share		Fair Value
Warrants to purchase		Issuance	Expiration
Common stock		7/19/2013	7/22/2023	[a]	101,010	$	3.96	$	244	[b]
Common stock		11/26/2014	11/26/2024	[a]	21,928	$	3.42	$	47	[b]
Common stock		3/1/2017	3/1/2027	[a]	1,388	$	5.94	$	5	[b]
Total common stock warrants					124,326
Redeemable convertible preferred stock	Series 5	7/1/2012	7/25/2019	[d]	54,917	$	9.10	$	255	[c]
Redeemable convertible preferred stock	Series 5	7/19/2013	7/22/2023	[e]	21,989	$	9.10	$	122	[c]
Redeemable convertible preferred stock	Series 6	11/26/2014	11/26/2024	[e]	6,310	$	16.47	$	49	[c]
Redeemable convertible preferred stock	Series 6	10/20/2015	10/20/2025	[e]	39,339	$	16.47	$	396	[c]
Redeemable convertible preferred stock	Series 6	11/9/2015	11/9/2025	[e]	24,283	$	16.47	$	244	[c]
Redeemable convertible preferred stock	Series 7	12/22/2016	12/22/2026	[e]	9,712	$	10.03	$	45	[c]
Total redeemable convertible preferred stock warrants					156,550
Total outstanding common and redeemable convertible preferred stock warrants					280,876

[a] Common stock warrants will remain outstanding until exercised by the holder.

[b] Fair value at the date of issuance.

[c] Fair value as of December 31, 2017.

[d] These warrants will be net exercised immediately upon the closing of the Company’s IPO, or upon a corporate transaction as defined in the Note and Warrant Purchase Agreement dated July 25, 2012.

[e] Convertible preferred stock warrants will remain outstanding until exercised by the holder and will convert to common stock warrants upon an IPO. The warrants will be exercisable for 10 years from the date of issuance.

Schedule of Weighted-Average Assumptions Used In Computation of Fair Value of Warrants

Weighted-average assumptions used in computation of the fair value of the redeemable convertible preferred stock warrants are summarized in the table below:

	Year Ended December 31,
	2018		2017
Remaining contractual term (in years)	4.9		5.3
Expected volatility	53.89	%	59.06	%
Risk-free interest rate	2.62	%	2.16	%
Dividend yield	—	%	—	%