Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2020

Stock-Based Compensation Expense

The following table presents stock-based compensation expense in the Company’s consolidated statements of comprehensive income:

	For the Years Ended December 31,
	2020		2019		2018
	(Amounts in thousands)
Cost of product revenue	$	1,929	$	1,368	$	1,019
Research and development		1,534		1,373		917
Selling, general and administrative		13,544		10,106		8,256
Total stock-based compensation	$	17,007	$	12,847	$	10,192

Estimated Weighted Average Assumptions

The fair value of share-based awards granted during the years ended December 31, 2020, 2019 and 2018 were calculated using the following estimated assumptions:

	For the Years Ended December 31,
	2020	2019	2018
Expected term (in years)	5.5-6.5	5.5-6.5	5.5-7.5
Expected volatility (range)	45.14 – 50.87%	45.14 – 50.87%	45.14 – 50.87%
Risk-free interest rate	0.34 – 1.15%	1.55 – 2.56%	2.63 – 2.96%
Expected dividend yield	0%	0%	0%

Summary of Option Activity

Information regarding option activity for the year ended December 31, 2020 under the Plans is summarized below:

	Shares			Weighted average exercise price		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value (in Thousands)
Options outstanding at December 31, 2019		957,559		$	30.81
Granted		79,698		$	115.81
Exercised		(340,546	)	$	23.95
Forfeited/expired/cancelled		—		$	—
Options outstanding at December 31, 2020		696,711		$	43.88		6.90	$	102,958
Options exercisable at December 31, 2020		311,988		$	31.75		5.91	$	49,879
Vested and expected to vest at December 31, 2020(1)		667,220					6.86	$	99,096

(1) Represents the number of vested options as of December 31, 2020 plus the number of unvested options expected to vest as of December 31, 2020 based on the unvested outstanding options at December 31, 2020 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.

Summary of Restricted Stock Unit Activity

The fair value of stock units is calculated using the closing price of the Company’s common stock on the date of grant. Information regarding stock unit activity, which includes activity for restricted stock units and performance stock units, for the year ended December 31, 2020 under the Plans is summarized below:

	Shares			Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value (in Thousands)
Unvested at December 31, 2019		734,984
Awarded		207,788
Vested		(244,648	)
Forfeited/expired/cancelled		(32,584	)
Unvested at December 31, 2020		665,540			3.32	$	127,904
Vested and expected to vest at December 31, 2020(1)		650,047			3.01	$	124,568

(1) Represents the number of vested stock units as of December 31, 2020 plus the number of unvested stock units expected to vest as of December 31, 2020 based on the unvested outstanding stock units at December 31, 2020 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.