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 months ended March 31, 2020 and 2019:


	Three Months Ended March 31,
	2020		2019

	(In thousands)
Cost of product and service revenues	$	1,770	$	1,462
Research and development	1,768		1,702
Selling, general, and administrative	7,121		5,246
Total share-based compensation expense	$	10,659	$	8,410

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 months ended March 31, 2020 and 2019:


	Three Months Ended March 31,
	2020		2019

Stock options
Expected life, years	4.7		4.5
Expected volatility, %	33.6	%	33.1	%
Risk-free interest rate, %	1.4	%	2.6	%
Estimated forfeiture rate, %	5.7	%	7.2	%
Dividend yield, %	—	%	—	%


	Three Months Ended March 31,
	2020		2019

Employee stock purchase plan shares
Expected life, years	0.5 - 2.0		0.5 - 2.0
Expected volatility, %	30.4% - 39.9%		28.2% - 38.4%
Risk-free interest rate, %	1.4% - 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 three months ended March 31, 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	430	85.32
Exercised	(227)	36.20
Expired	(2)	51.50
Forfeited	(65)	64.06
Outstanding at March 31, 2020	4,038	$	56.96	7.8	$	57,180
Exercisable at March 31, 2020	1,586	$	39.38	6.3	$	42,826
Vested and expected to vest at March 31, 2020 and thereafter	3,846	$	56.18	7.7	$	56,526

The weighted-average fair value per share of options granted during the three months ended March 31, 2020 and 2019 was $26.31 and $24.07, respectively. The intrinsic value of options exercised during the three months ended March 31, 2020 and 2019 was $9.9 million and $17.1 million, respectively.

As of March 31, 2020, total unrecognized compensation cost related to unvested stock options was $46.6 million, which is expected to be recognized over a weighted-average vesting period of 2.9 years.

For the three months ended March 31, 2020 and 2019, employees purchased approximately 217,000 and 210,000 shares of common stock, respectively, under the ESPP at weighted average prices of $43.51 and $40.20, respectively. As of March 31, 2020, the unrecognized compensation cost related to the shares to be purchased under the ESPP was approximately $7.7 million and is expected to be recognized over a weighted-average period of 1.4 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 three months ended March 31, 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)	62	85.05
Vested (Released)	(33)	54.41
Forfeited	(17)	66.06
Outstanding and unvested at March 31, 2020	556	$	69.44	1.6	$	36,482

As of March 31, 2020, total unrecognized compensation cost related to RSUs was $34.1 million, which is expected to be recognized over the remaining weighted-average vesting period of 3.0 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)	—	—
Vested (Released)	—	—

Outstanding and unvested at March 31, 2020	17	$	81.92

As of March 31, 2020, total unrecognized compensation cost related to RSAs was $0.2 million, which is expected to be recognized over the remaining weighted-average vesting period of 0.1 years.

A summary of the performance-based restricted stock activity under the 2009 Plan is presented below for the three months ended March 31, 2020:


	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	(15)	72.02
Forfeited	—	—
Outstanding and unvested at March 31, 2020	182	$	63.63

As of March 31, 2020, total unrecognized compensation cost related to PSUs was approximately $6.7 million, which is expected to be recognized over the remaining weighted-average vesting period of 1.5 years.


			Number of Shares

			(In thousands)
Share options outstanding			4,038
Non-vested restricted stock awards			755
Shares authorized for future issuance			2,252
ESPP shares available for future issuance			1,322
Total shares reserved for future issuance			8,367

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. As of March 31, 2020, the maximum dollar value of shares that may yet be purchased under the two repurchase programs 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.