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Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2020
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, 20204,192,122 $14.42 6.47$56,218 
Granted91,052 26.06 
Canceled and forfeited(169,049)16.55 
Exercised(1,483,602)12.64 
Outstanding at December 31, 20202,630,523 $15.68 5.84$134,670 
December 31, 2020:
Options vested and expected to vest2,630,523 $15.68 5.84$134,670 
Options exercisable1,901,861 $14.13 5.02$34,348 
Company's Options Outstanding
The following table summarizes information about the Company’s stock options outstanding at December 31, 2020: 
 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
686,488 4.81527,069 4.12
$12.77 – $14.99
584,628 4.74563,444 4.64
$15.21 – $18.55
344,177 4.41297,704 3.99
$18.68 – $22.71
393,152 6.55302,418 6.04
$23.00 – $29.13
622,078 8.33211,226 8.28
2,630,523 1,901,861 
Restricted Stock Units Award Activity
A summary of RSU activity under the Plans is as follows:
Non-vested RSUsShare EquivalentWeighted-Average Grant Date Fair Value
Non-vested at January 1, 20201,435,774 $18.69 
Changes during the year:
Granted824,827 29.15 
Vested(455,278)15.29 
Forfeited(200,601)21.98 
Non-vested at December 31, 20201,604,722 $24.61 
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 as follows (in thousands):
202020192018
Cost of revenue$983 $786 $616 
Research and development3,864 4,100 3,156 
Selling, general and administrative13,643 11,726 6,982 
Total stock-based compensation expense$18,490 $16,612 $10,754 
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:
202020192018
Risk-free interest rates
0.54% — 1.69%
1.41% — 2.56%
2.22% — 3.01%
Expected term (years)
6.08
5.12 — 6.08
5.50 — 6.09
Expected dividend yield—%—%—%
Expected volatility
53.0% — 59.6%
52.6% — 58.0%
56.0% — 57.7%