For the three months ended March 31, 2021, we recognized stock option expense of approximately $0.02 million. This stock option expense is related to stock options granted by Savitech Corporation (“Savitech”) in Savitech stock to their employees. We acquired a controlling interest in Savitech in 2020. The remainder of our share-based compensation expense was related to share grants. Approximately $0.8 million of cash proceeds were received from stock option exercises during the three months ended March 31, 2021. The table below sets forth the line items where share-based compensation expense was recorded:

	Three Months Ended
	March 31,
	2021		2020
Cost of goods sold	$	275	$	273
Selling, general and administrative		5,033		3,711
Research and development		814		709
Total share-based compensation expense	$	6,122	$	4,693

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 Company’s 2013 Equity Incentive Plan, and there will be no additional share grants under the 2001 Omnibus Equity Incentive 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.

As of March 31, 2021, total unrecognized share-based compensation expense related to share grants was approximately $52.2 million, before income taxes, and is expected to be recognized over a weighted average period of approximately 2.2 years.