Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Stock-Based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
	(Amounts in thousands)
Cost of product revenue	$	292	$	234	$	616	$	500
Research and development		319		227		641		397
Selling, general and administrative		2,420		2,164		5,026		3,996
Total stock-based compensation	$	3,031	$	2,625	$	6,283	$	4,893

Estimated Weighted Average Assumptions

Information regarding option activity for the six months ended June 30, 2019 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, 2018		998,226		$	27.54
Granted		44,996		$	61.98
Exercised		(57,956	)	$	9.75
Forfeited/expired/cancelled		—		$	—
Options outstanding at June 30, 2019		985,266		$	30.16		7.13	$	54,971
Options exercisable at June 30, 2019		521,884		$	23.80		5.85	$	32,437
Vested and expected to vest at June 30, 2019(1)		945,981					7.07	$	53,042

(1) Represents the number of vested options as of June 30, 2019 plus the number of unvested options expected to vest as of June 30, 2019 based on the unvested outstanding options at June 30, 2019 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

Information regarding RSU activity for the six months ended June 30, 2019 under the Plans is summarized below:

	Shares			Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value (in Thousands)
Unvested at December 31, 2018		707,413
Awarded		266,329
Vested		(187,617	)
Forfeited/expired/cancelled		(19,139	)
Unvested at June 30, 2019		766,986			3.85	$	65,922