7. Stockholders’ Equity

Stock-based Compensation

As of March 31, 2019, we maintained the Amended and Restated 2012 Incentive Award Plan (the “2012 Plan”) and the Amended and Restated 2006 Equity Participation Plan (“2006 Plan”) as stock-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 stock-based employee compensation plans: the AS&E 2005 Equity and Incentive Plan and the AS&E 2014 Equity and Incentive Plan (collectively the " AS&E Plans”). No new equity grants will be made under the AS&E Plans. The 2012 Plan, the 2006 Plan, and the AS&E Plans are collectively referred to as the “OSI Plans”.

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


	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2019		2018		2019
Cost of goods sold	$	251	$	182	$	739	$	539
Selling, general and administrative		5,614		5,543		16,574		18,487
Research and development		149		163		441		488
Stock-based compensation expense	$	6,014	$	5,888	$	17,754	$	19,514

As of March 31, 2019, total unrecognized compensation cost related to stock-based compensation grants under the OSI Plans were estimated at $0.6 million for stock options and $19.4 million for RSUs. We expect to recognize these costs over a weighted average period of 2.0 years with respect to the stock options and 1.9 years for grants of RSUs.

The following summarizes stock option activity during the nine months ended March 31, 2019:


		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	18,135	$	72.39
Exercised	(108,008)	$	22.82
Expired or forfeited	(9,618)	$	70.28
Outstanding at March 31, 2019	578,034	$	35.29	2.6 years	$	30,247
Exercisable at March 31, 2019	540,646	$	32.37	2.1 years	$	29,865

The following summarizes RSU award activity during the nine months ended March 31, 2019:


		Weighted-
		Average
	Shares	Fair Value
Nonvested at June 30, 2018	526,377	$	71.56
Granted	362,025		73.80
Vested	(357,924)		71.01
Forfeited	(13,669)		73.74
Nonvested at March 31, 2019	516,809	$	73.45

As of March 31, 2019, there were approximately 1.6 million shares available for grant under the 2012 Plan. Under the terms of the 2012 Plan, RSUs granted from the pool of shares available for grant reduce the pool by 1.87 shares for each award granted. RSUs 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 97,514 performance-based RSUs during the nine months ended March 31, 2018 and 2019, 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, our 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.

We did not repurchase any shares during the three months ended March 31, 2019. During the nine months ended March 31, 2019, we repurchased 288,316 shares of our common stock, and as of March 31, 2019, there were 562,707 shares available to repurchase under the program.