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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2021
Share-based Payment Arrangement [Abstract]  
Schedule of Stock-Based Compensation Expense We report our stock-based compensation expense (inclusive of our incentive stock plan and employee stock purchase plan) in the accompanying Consolidated Statements of Operations within “total operating costs and expenses” for the years ended December 31, 2021 and 2020, as follows:
Year Ended December 31,
20212020
Selling, general and administrative$14,642 $13,127 
Research and development5,197 4,692 
Total stock-based compensation$19,839 $17,819 
Schedule of Fair Value of Stock Options Granted Using Black-Scholes Option Pricing Model
The fair value of stock options granted was estimated at the date of grant using the Black-Scholes option-pricing model. The following assumptions were used to determine fair value for the stock awards granted in the applicable year:
Year Ended December 31,
20212020
Expected option life (in years)(a)
5.575.46
Risk-free interest rate(b)
0.56% - 1.32%
0.34% - 1.61%
Volatility(c)
80.0% - 82.7%
74.5% - 81.4%
Dividend yield(d)
0%0%
Weighted-average grant-date fair value per stock option$1.78$1.63
(a)Determined by the historical stock option exercise behavior of our employees (maximum term is 10 years).
(b) Based upon the U.S. Treasury yields in effect during the period which the options were granted (for a period equaling the stock options’ expected term).
(c)Measured using our historical stock price for a period equal to stock options’ expected term.
(d)We do not expect to declare any cash dividends in the foreseeable future.
Schedule of Stock Option Activity
Stock option activity during the years ended December 31, 2021 and 2020 was as follows:
Number of
Shares		Weighted-
Average
Exercise
Price/Share		Weighted-
Average
Remaining
Contractual
Term (Years)		Aggregate
Intrinsic
Value
Outstanding — December 31, 20196,439,936 $9.61 
Granted2,032,000 2.34 
Exercised(3,542)3.70 $708 (1)
Forfeited(170,187)8.29 
Expired(641,584)8.55 
Outstanding — December 31, 20207,656,623 $7.80 
Granted2,397,684 2.66 
Exercised(1,250)3.04 $1.5 (1)
Forfeited(34,565)10.05 
Expired(513,031)9.29 
Outstanding — December 31, 20219,505,461 $6.42 5.86$— (2)
Vested (exercisable) — December 31, 20216,371,266 $8.04 4.26$— (2)
Unvested (unexercisable) — December 31, 20213,134,195 $3.13 9.10$— (2)
(1) Represents the total difference between our closing stock price at the time of exercise and the stock option exercise price, multiplied by the number of options exercised.
(2) Represents the total difference between our closing stock price on the last trading day of 2021 and the stock option exercise price, multiplied by the number of in-the-money options as of December 31, 2021. The amount of intrinsic value will change based on the fair market value of our stock.
Schedule of Stock Option Grants The following table summarizes information with respect to stock option grants as of December 31, 2021:
OutstandingExercisable
Exercise PriceGranted Stock
Options
Outstanding		Weighted-
Average
Remaining
Contractual
Life (Years)		Weighted-
Average
Exercise
Price		Granted
Stock
Options
Exercisable		Weighted-
Average
Exercise
Price
$1.29 - 4.96
4,397,491 7.6$2.52 1,507,886 $2.58 
$4.97 - 6.91
1,854,119 4.336.00 1,854,119 6.00 
$6.92 - 9.00
1,376,034 3.417.80 1,300,617 7.77 
$9.01 - 12.00
925,709 4.1711.17 769,707 11.17 
$12.01 - 22.64
952,108 5.9918.61 938,937 18.63 
9,505,461 5.86$6.42 6,371,266 $8.04 
Schedule of Restricted Stock Award and Restricted Stock Units Activity A summary of restricted stock award activity is as follows:
Number of
Restricted Stock
Awards		Weighted Average
Fair Value per
Share at Grant
Date
Unvested — December 31, 20191,659,759 $11.67 
Granted4,026,518 2.68 
Vested(753,475)11.23 
Forfeited(436,757)6.03 
Unvested — December 31, 20204,496,045 4.29 
Granted2,820,259 3.33 
Vested(2,272,064)5.06 
Forfeited(608,233)3.85 
Unvested — December 31, 20214,436,007 $3.33 
A summary of restricted stock unit activity is as follows:
Number of
Restricted Stock
Units		Weighted Average
Fair Value per
Share at Grant
Date
Outstanding — December 31, 2019385,919 $18.00 
Granted6,800 2.36 
Market-based achievement adjustment at vesting(128,334)— 
Share issuance(861)10.69 
Outstanding — December 31, 2020263,524 26.39 
Granted2,125 3.61 
Market-based achievement adjustment at vesting75,000 — 
Share issuance(151,386)28.09 
Forfeited(4,751)4.03 
Outstanding — December 31, 2021184,512 $23.53