Equity Plans and Stock-Based Compensation

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement, Noncash Expense [Abstract]

Equity Plans and Stock-Based Compensation

11. Equity Plans and Stock-Based Compensation

As of March 31, 2022, the 2018 Equity Incentive Plan, as amended (“Amended 2018 EIP”), the Amended 2021 Inducement Plan and the Amended and Restated 2014 Employee Stock Purchase Plan are our active plans. Under the Amended 2018 EIP, the aggregate number of shares of our common stock that may be issued to employees and directors (subject to adjustment for certain changes in capitalization) is 22,517,869.

The Amended 2018 EIP is administered by our Board of Directors, or a designated committee of the Board of Directors, and awards granted under the Amended 2018 EIP have a term of 7 years unless earlier terminated by the Board of Directors. As of March 31, 2022, there were 785,592 shares of common stock reserved for issuance under the Amended 2018 EIP.

Activity under our stock plans is set forth below:


	Shares Underlying Outstanding Options (in thousands)			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Balance as of December 31, 2021		10,399		$	11.55		4.16		42,756
Options granted		1,793			12.70
Options exercised		(155	)		7.24
Options cancelled:
Options forfeited (unvested)		(25	)		9.40
Options expired (vested)		(38	)		35.48
Balance as of March 31, 2022		11,974		$	11.71		4.58	$	20,270
Vested and expected to vest as of March 31, 2022		11,494		$	11.70		4.31	$	19,947
Exercisable as of March 31 2022		6,473		$	12.48		3.09	$	13,042

Restricted stock unit activity under our stock-based compensation plans during the three months ended March 31, 2022 was as follows (in thousands except per share amounts):


	Number of Shares (in thousands)			Weighted-Average Grant-Date Fair Value Per Share
Non-vested as of December 31, 2021		2,651		$	8.30
Granted		1,761			12.65
Vested		(999	)		8.25
Forfeited		(24	)		11.49
Non-vested as of March 31, 2022		3,389		$	10.56

We granted performance-based restricted stock unit (“PSU”) to certain executives. These PSUs vest upon a specified market condition. The summary of PSU activities for the three months ended March 31, 2022 is as follows:


	Number of Shares (in thousands)			Weighted-Average Grant-Date Fair Value Per Share
Non-vested as of December 31, 2021		237		$	8.40
Granted		193			11.62
Vested		(237	)		8.40
Non-vested as of March 31, 2022		193		$	11.62

The fair value-based measurement of each option is estimated on the date of grant using the Black-Scholes option valuation model. The fair value of each RSU is determined at the date of grant using our closing stock price. The fair value of each PSU is estimated using the Monte Carlo simulation method on the date of grant. The weighted-average assumptions used in the calculations of these fair value measurements are as follows:


	Stock Options						Market-Based Performance Stock Unit (“PSUs”)
	Three Months Ended						Three Months Ended
	March 31,						March 31,
	2022			2021			2022
Weighted-average fair value per share	$	8.05		$	6.72		$	11.62
Risk-free interest rate		1.9	%		0.5	%		1.7	%
Expected life (in years)		4.5			4.5			2.9
Volatility		0.8			1.0			0.9

The components of stock-based compensation expense were as follows (in thousands):


	Three Months Ended
	March 31,
	2022		2021
Research and development	$	1,276	$	872
Selling, general and administrative		5,427		3,144
Cost of sales - product		160		170
Inventory		783		537
Total	$	7,646	$	4,723

Compensation expense is based on awards ultimately expected to vest and reflects estimated forfeitures.