Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2020

Stock-Based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
	(Amounts in thousands)
Cost of product revenue	$	425	$	292	$	858	$	616
Research and development		394		319		766		641
Selling, general and administrative		3,283		2,420		6,643		5,026
Total stock-based compensation	$	4,102	$	3,031	$	8,267	$	6,283

Summary of Option Activity

Information regarding option activity for the six months ended June 30, 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		57,698		$	100.53
Exercised		(246,353	)	$	21.97
Forfeited/expired/cancelled		—		$	—
Options outstanding at June 30, 2020		768,904		$	38.87		7.14	$	65,243
Options exercisable at June 30, 2020		392,181		$	30.64		6.26	$	36,463
Vested and expected to vest at June 30, 2020(1)		738,412					7.10	$	62,833

(1) Represents the number of vested options as of June 30, 2020 plus the number of unvested options expected to vest as of June 30, 2020 based on the unvested outstanding options at June 30, 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 six months ended June 30, 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		149,755
Vested		(170,778	)
Forfeited/expired/cancelled		(17,863	)
Unvested at June 30, 2020		696,098			3.59	$	86,045
Vested and expected to vest at June 30, 2020(1)		641,476			3.28	$	79,293

(1) Represents the number of vested stock units as of June 30, 2020 plus the number of unvested stock units expected to vest as of June 30, 2020 based on the unvested outstanding stock units at June 30, 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.