7. Stockholders’ Equity

Stock-based Compensation

On December 11, 2017, our stockholders approved our Amended and Restated 2012 Incentive Award Plan (the “2012 Plan"). As of September 30, 2018, we maintained the 2012 Plan and the Amended and Restated 2006 Equity Participation Plan (“2006 Plan”) as share-based employee compensation plans. No further grants may be made under the 2006 Plan. In addition, pursuant to the acquisition of American Science and Engineering, Inc. (“AS&E”), we assumed two share based employee compensation plans: the AS&E 2005 Equity and Incentive Plan (“2005 AS&E Plan”) and the AS&E 2014 Equity and Incentive Plan (“2014 AS&E Plan”). No new RSU grants will be made under the 2005 AS&E Plan or the 2014 AS&E Plan. The 2012 Plan, the 2006 Plan, the 2005 AS&E Plan and the 2014 AS&E Plan are collectively referred to as the “OSI Plans”.

We recorded stock-based compensation expense in the consolidated statement of operations as follows (in thousands):


	Three Months Ended September 30,
	2017		2018
Cost of goods sold	$	241	$	207
Selling, general and administrative		5,111		5,111
Research and development		135		145
Stock-based compensation expense, before taxes		5,487		5,463
Less: related income tax benefit		(1,693)		(1,341)
Stock-based compensation expense, net of estimated taxes	$	3,794	$	4,122

As of September 30, 2018, total unrecognized compensation cost related to share-based compensation grants under the OSI Plans were estimated at $0.5 million for stock options and $29.0 million for RSUs. We expect to recognize these costs over a weighted average period of 1.8 years with respect to the stock options and 1.7 years for grants of RSUs.

The following summarizes stock option activity during the three months ended September 30, 2018:


		Weighted Average		Weighted-Average		Aggregate
	Number of	Exercise		Remaining Contractual		Intrinsic Value
	Options	Price		Term		(in thousands)
Outstanding at June 30, 2018	677,525	$	32.80
Granted	—	$	—
Exercised	(9,034)	$	41.32
Expired or forfeited	(4,741)	$	68.64
Outstanding at September 30, 2018	663,750	$	32.43		2.6 years	$	29,344
Exercisable at September 30, 2018	632,251	$	29.95		2.3 years	$	29,317

The following summarizes RSU award activity during the three months ended September 30, 2018:


		Weighted-
		Average
	Shares	Fair Value
Nonvested at June 30, 2018	526,377	$	71.56
Granted	323,141	$	73.80
Vested	(340,082)	$	70.68
Forfeited	(8,957)	$	72.95
Nonvested at September 30, 2018	500,479	$	73.58

As of September 30, 2018, there were approximately 1.7 million shares available for grant under the 2012 Plan. Under the terms of the 2012 Plan, RSUs and restricted stock granted from the pool of shares available for grant reduce the pool by 1.87 shares for each award granted. RSUs and restricted stock forfeited and returned to the pool of shares available for grant increase the pool by 1.87 shares for each award forfeited.

We granted 117,346 and 96,151 performance-based RSUs during the three months ended September 30, 2017 and 2018, respectively. These performance based RSU awards are contingent on the achievement of certain performance metrics. The payout related to these awards can range from zero to 280% of the original number of shares or units awarded.

Share Repurchase Program

In March 2018, the Board of Directors authorized a share repurchase program of up to 1,000,000 shares. This program does not expire unless our Board of Directors acts to terminate the program. The timing and actual number of shares purchased depend on a variety of factors, including stock price, general business and market conditions and other investment opportunities and may be purchased through the open market. Upon repurchase, the shares are restored to the status of authorized but unissued, and we record them as a reduction in the number of shares of common stock issued and outstanding in our consolidated financial statements.

During the three months ended September 30, 2018, we repurchased 104,146 shares of our common stock.