STOCKHOLDERS' EQUITY (DEFICIT) (Tables)

6 Months Ended

Jun. 30, 2021

Equity [Abstract]

Summary of Common Stock

In addition, the Company had reserved for issuance the following number of shares of common stock for the purposes described below as of June 30, 2021 and December 31, 2020 (in thousands):

	June 30, 2021	December 31, 2020
Shares of common stock issued	188,461	140,450
Shares of common stock reserved for issuance for:
Warrants	1,394	2,247
Stock options	17,349	10,147
Shares available for grant under 2014 Stock Incentive Plan	12,290	4,863
Shares available for sale under 2014 Employee Stock Purchase Plan	2,300	—
Total shares of common stock issued and reserved for issuance	221,794	157,707

Summary of Warrants Outstanding and Warrant Activity

The following table sets forth the Company's warrant activity for the six months ended June 30, 2021 (in thousands):

			Year-to-Date Warrant Activity
Issued	Exercise Price	Expiration	December 31, 2020	Issued	(Exercised)	(Expired)	June 30, 2021
Jun-2019	$1.47	Jun-2020	—	—	—	—	—
Mar-2018	$0.55*	Mar-2023	1,705	—	(378)	—	1,327
Nov-2017	$0.55*	Nov-2022	487	—	(475)	—	12
May-2015	$11.83	Nov-2024	28	—	—	—	28
Nov-2014	$11.04	Nov-2024	27	—	—	—	27
			2,247	—	(853)	—	1,394

* Exercise price shown (i) reflects modification (ii) subject to further adjustment based on down round provision added by amendment described in "Item 15. Exhibits and Financial Statement Schedules - Note. 10 Stockholders' (Deficit) Equity" in the audited annual consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2020.