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Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2021
Share-based Payment Arrangement [Abstract]  
Stock Option Activity and Related Information
A summary of the Company’s stock option activity under the Plans is as follows:
SharesWeighted-
average exercise
price per share		Weighted-
average remaining
contractual
term (in years)		Aggregate
intrinsic value
(in thousands)
Outstanding at January 1, 20212,630,523 $15.68 5.84$134,670 
Canceled and forfeited(42,329)14.88 
Exercised(570,403)11.35 
Outstanding at December 31, 20212,017,791 $16.93 5.25$51,105 
December 31, 2021:
Options vested and expected to vest2,017,791 $16.93 5.25$51,105 
Options exercisable1,716,159 $15.79 4.86$5,730 
Company's Options Outstanding
The following table summarizes information about the Company’s stock options outstanding at December 31, 2021: 
 OutstandingExercisable
Exercise PriceNumber of
Shares		Weighted-
Average
Remaining
Contractual
Life in Years		Number of
Shares		Weighted-
Average
Remaining
Contractual
Life in Years
$1.92 – $12.56
381,265 4.99362,291 4.93
$12.77 – $14.99
494,527 3.69489,955 3.66
$15.21 – $18.55
238,237 3.43228,621 3.29
$18.68 – $22.71
343,952 5.46297,292 5.11
$23.00 – $72.33
559,810 7.46338,000 7.37
2,017,791 1,716,159 
Restricted Stock Units Award Activity
A summary of RSU and PSU activity under the Plans is as follows:
Non-vested RSUs and PSUsShare EquivalentWeighted-Average Grant Date Fair Value
Non-vested at January 1, 20211,604,722 $24.61 
Changes during the year:
Granted544,292 65.76 
Vested(694,168)22.04 
Forfeited(121,631)40.22 
Non-vested at December 31, 20211,333,215 $41.32 
Stock Compensation Expense
The following table sets forth stock-based compensation expense related to stock-based arrangements under the Plans as presented within the consolidated statement of operations for the years ended December 31 (in thousands):
202120202019
Cost of product and service revenue$1,870 $983 $786 
Research and development5,723 3,864 4,100 
Selling, general and administrative21,270 13,643 11,726 
Total stock-based compensation expense$28,863 $18,490 $16,612 
Fair Value of Employee Option Grant The fair value of each employee stock option grant was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions:
20202019
Risk-free interest rates
0.54% — 1.69%
1.41% — 2.56%
Expected term (years)
6.08 — 6.08
5.12 — 6.08
Expected dividend yield—%—%
Expected volatility
53.0% — 59.6%
52.6% — 58.0%