The table below sets forth the line items where share-based compensation expense was recorded for the twelve months ended December 31:

	2020		2019		2018
Cost of goods sold	$	1,064	$	925	$	362
Selling, general and administrative expense		21,013		16,687		17,395
Research and development expense		3,183		2,923		2,979
Total share-based compensation expense	$	25,260	$	20,535	$	20,736

The table below sets forth share-based compensation expense by type for the twelve months ended December 31:

	2020		2019		2018
Stock options	$	-	$	-	$	274
Share grants		25,260		20,535		20,462
Total share-based compensation expense	$	25,260	$	20,535	$	20,736

In May 2013, our stockholders approved our 2013 Equity Incentive Plan (“2013 Plan”). Since the approval of the 2013 Plan, all stock options are granted under the 2013 Plan, and we will not grant any further stock options under our 2001 Plan. Stock options under the 2013 Plan generally vest in equal annual installments over a four-year period and expire eight years after the grant date. The number of shares originally authorized to be awarded under the 2013 Plan was 6 million shares. In May 2017, our stockholders approved an amendment to the 2013 Plan, authorizing and additional 6 million shares to be awarded, bringing the total shares authorized to be awarded under the 2013 Plan to 12 million shares.

Share-based compensation expense for stock options granted in previous years was calculated on the date of grant using the Black-Scholes-Merton option-pricing model. No stock options were granted in any of the periods presented.

Total cash received from option exercises was approximately $6.8 million, $11.9 million and $4.9 million during 2020, 2019 and 2018, respectively.

At December 31, 2020, there was no unrecognized compensation expense related to unvested options.

Stock Options	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2017		1,228			22.85
Exercised		(240	)		20.28
Outstanding at December 31, 2018		988			23.47			$	8,693
Exercised		(524	)		22.68			$	10,600
Outstanding and Exercisable at December 31, 2019		464			24.37			$	14,849
Exercised		(272	)		25.11			$	8,278
Outstanding and Exercisable at December 31, 2020		192			23.32		1.4	$	9,059

The table below sets forth information about stock options outstanding at December 31, 2020:

Plan

Range of Exercise Prices

Number Exercisable

Weighted Average Remaining Contractual Life

(Years)

Weighted Average Exercise Price

2001 Plan

18.48 - 19.27

102

1.4

19.25

2013 Plan

27.92

1.4

27.92

Share Grants – Restricted stock awards and restricted stock units generally vest in equal annual installments over a four-year period. All new grants are granted under the 2013 Plan, and there will be no additional share grants under the 2001 Plan. Restricted stock grants are measured based on the fair market value of the underlying stock on the date of grant and compensation expense is recognized on a straight-line basis over the requisite four-year service period.

Performance stock units (“PSUs”) are measured based on the fair market value of the underlying stock on the date of grant and compensation expense is recognized over the three-year performance period, with adjustments made to the expense to recognize the probable payout percentage. PSUs will vest upon the Company achieving a cumulative 3-year non-GAAP operating income target for the applicable periods.

The table below sets forth a summary of our non-vested share grants in 2020, 2019 and 2018:

Nonvested at December 31, 2017	2,280		22.24
Granted	646		32.06
Vested	(1,213	)	21.39
Forfeited	(46	)	24.72
Nonvested at December 31, 2018	1,667		26.68
Granted	670		38.15
Vested	(573	)	24.90
Forfeited	(67	)	30.44
Nonvested at December 31, 2019	1,697		31.71
Granted	573		48.83
Vested	(770	)	27.78	$	37,620
Forfeited and other	88		38.31
Nonvested at December 31, 2020	1,588		39.30	$	111,947

During 2020, in connection with the retirement of a member of the Company’s board of directors, the Company modified that director’s unvested RSU grants to vest upon his retirement. The shares subject to the modified grants will be released to that board member as if they were vesting under the original vesting timeline. In connection with this modification, the Company recorded additional expense of approximately $1.7 million. During 2018, we modified previously granted stock option and stock awards for two corporate officers who retired. The result of the modification was the acceleration of the vesting of 7,500 stock options and 79,720 stock awards for the corporate officers. The incremental expense recorded for this modification was approximately $1.8 million, which was expensed in SG&A during 2018

The total unrecognized share-based compensation expense as of December 31, 2020, was approximately $44.8 million, relating to share grants, which was expected to be recognized over a weighted average period of approximately 2.2 years. The aggregate fair value amount of share grants that vested during 2020 was $37.6 million.