For a detailed explanation of the Company's stock plans, refer to Note 13, Employee Benefits and Share-Based Compensation, of the Company's annual report on Form 10-K for the year ended December 31, 2019 filed with the SEC on February 26, 2020.

The following table sets forth the total share-based compensation expense recognized in the Company’s Condensed Consolidated Statements of Operations for the three and nine months ended September 30, 2020 and 2019:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019

	(In thousands)
Cost of product and service revenues	$	1,758	$	1,316	$	5,658	$	4,194
Research and development	1,577		1,652		5,199		4,938
Selling, general, and administrative	7,689		5,537		22,177		16,043
Total share-based compensation expense	$	11,024	$	8,505	$	33,034	$	25,175

The following assumptions were used to value stock options and Employee Stock Purchase Plan (“ESPP”) shares granted pursuant to the Company’s equity incentive plans for the three and nine months ended September 30, 2020 and 2019:


	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019

Stock options
Expected life, years	4.7		4.3		4.7		4.4
Expected volatility, %	41.2	%	34.7	%	39.0	%	33.7	%
Risk-free interest rate, %	0.3	%	1.6	%	0.7	%	2.1	%
Estimated forfeiture rate, %	5.7	%	7.2	%	5.7	%	7.2	%
Dividend yield, %	—	%	—	%	—	%	—	%


	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019

Employee stock purchase plan shares
Expected life, years	0.5 - 2.0		0.5 - 2.0		0.5 - 2.0		0.5 - 2.0
Expected volatility, %	30.4% - 53.5%		28.9% - 39.9%		30.4% - 53.5%		28.2% - 39.9%
Risk-free interest rate, %	0.1% - 2.7%		1.4% - 2.7%		0.1% - 2.7%		1.3% - 2.7%
Dividend yield, %	—	%	—	%	—	%	—	%

The following table summarizes the share option activity under the Company’s equity incentive plans during the nine months ended September 30, 2020:


	Number of Shares	Weighted-Average Exercise Price		Weighted-Average Remaining Years	Aggregate Intrinsic Value

	(In thousands, except per share data)
Outstanding at December 31, 2019	3,902	$	52.75	7.7	$	113,198
Granted	1,065	75.92
Exercised	(446)	38.10
Expired	(11)	59.08
Forfeited	(356)	65.84
Outstanding at September 30, 2020	4,154	$	59.12	7.6	$	72,331
Exercisable at September 30, 2020	1,763	$	43.38	6.0	$	55,936
Vested and expected to vest at September 30, 2020 and thereafter	3,973	$	58.49	7.5	$	71,456

The weighted-average fair value per share of options granted during the three months ended September 30, 2020 and 2019 was $23.75 and $21.59, respectively, and the weighted-average fair value per share of options granted during the nine months ended September 30, 2020 and 2019 was $25.30 and $23.41, respectively. The intrinsic value of options exercised during the three months ended September 30, 2020 and 2019 was $4.1 million and $2.7 million, respectively, and during the nine months ended September 30, 2020 and 2019 was $16.5 million and $27.0 million, respectively.

As of September 30, 2020, total unrecognized compensation cost related to unvested stock options was $50.4 million, which is expected to be recognized over a weighted-average vesting period of 2.9 years.

For the nine months ended September 30, 2020 and 2019, employees purchased approximately 333,000 and 374,000 shares of common stock, respectively, under the ESPP at weighted average prices of $48.77 and $41.44, respectively. As of September 30, 2020, the unrecognized compensation cost related to the shares to be purchased under the ESPP was approximately $6.2 million and is expected to be recognized over a weighted-average period of 1.5 years.

Summaries of the restricted stock activity under the Company’s 2009 Equity Incentive Plan, as amended (the “2009 Plan”) are presented below for the nine months ended September 30, 2020:


	Number of Shares	Weighted-Average Grant Date Fair Value		Weighted-Average Remaining Years	Aggregate Intrinsic Value

	(In thousands, except per share data)
Restricted stock units
Outstanding at December 31, 2019	544	$	66.65	1.6	$	44,492
Granted (Awarded)	285	72.10
Vested (Released)	(107)	56.60
Forfeited	(104)	66.12
Outstanding and unvested at September 30, 2020	618	$	71.00	1.6	$	46,114

As of September 30, 2020, total unrecognized compensation cost related to RSUs was $40.3 million, which is expected to be recognized over the remaining weighted-average vesting period of 3.1 years.


	Number of Shares	Weighted-Average Grant Date Fair Value

	(In thousands, except per share data)
Restricted stock awards
Outstanding at December 31, 2019	17	$	81.92
Granted (Awarded)	21	68.11
Vested (Released)	(17)	81.92

Outstanding and unvested at September 30, 2020	21	$	68.11

As of September 30, 2020, total unrecognized compensation cost related to RSAs was $0.9 million, which is expected to be recognized over the remaining weighted-average vesting period of 0.6 years.


	Number of Shares	Weighted-Average Grant Date Fair Value Per Unit

	(In thousands, except per share data)
Outstanding at December 31, 2019	134	$	55.82
Granted	63	82.41
Vested	(44)	54.25
Forfeited	(5)	81.72
Outstanding and unvested at September 30, 2020	148	$	66.69

As of September 30, 2020, total unrecognized compensation cost related to PSUs was approximately $4.4 million, which is expected to be recognized over the remaining weighted-average vesting period of 1.2 years.


			Number of Shares

			(In thousands)
Share options outstanding			4,154
Non-vested restricted stock awards			787
Shares authorized for future issuance			1,553
ESPP shares available for future issuance			1,206
Total shares reserved for future issuance			7,700

On August 2, 2016, the Company's Board of Directors (the “Board”) authorized a stock repurchase program providing for the repurchase of up to $50.0 million of the Company’s common stock (the “2016 Repurchase Program”). The 2016 Repurchase Program is in addition to the stock repurchase program approved by the Board on November 4, 2014 (the “2014 Repurchase Program”). As of September 30, 2020, the maximum dollar value of shares that may yet be purchased under the 2014 Repurchase Program and the 2016 Repurchase Program was $54.9 million. The stock repurchase programs do not obligate the Company to repurchase any specific number of shares, and the Company may terminate or suspend the repurchase programs at any time.

On September 17, 2020, the Board authorized a one-time stock repurchase transaction providing for the repurchase of up to $75.0 million of the Company’s common stock in privately negotiated transactions concurrently with the issuance of the Notes, described in Note 9, Convertible Senior Notes. In September 2020, the Company repurchased 749,300 shares of its common stock from purchasers of the Notes in the offering in privately negotiated transactions effected through one of the initial purchasers or its affiliate at an average price of $70.78 per share for an aggregate purchase price of approximately $53.0 million. There will be no further repurchases under this one-time authorization.

During the three and nine months ended September 30, 2020 and 2019, the Company did not repurchase any of its outstanding common stock including under the 2014 Repurchase Program and the 2016 Repurchase Program, other than the separately-authorized one-time stock repurchase concurrent with the offering of the Notes in September 2020.