10. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Tables)

12 Months Ended

May 31, 2018

Equity [Abstract]

Changes in the components of AOCI

    Changes in the components of AOCI, net of tax, were as follows (in thousands):

	Cumulative Translation Adjustments		Unrealized Loss on Investments, Net		Total
Balance at May 31, 2016	$	2,237	$	—	$	2,237
Other comprehensive income (loss) before reclassification		12		—		12
Amounts reclassified out of AOCI		—		—		—
Other comprehensive income (loss), net of tax		12		—		12
Balance at May 31, 2017	$	2,249	$	—	$	2,249
Other comprehensive income (loss) before reclassifications		43		—		43
Amounts reclassified out of AOCI		—		—		—
Other comprehensive income (loss), net of tax		43		—		43
Balance at May 31, 2018	$	2,292	$	—	$	2,292

Compensation costs related to the Company's stock-based compensation

    The following table summarizes the stock-based compensation expense for the years ended May 31, 2018, 2017 and 2016 (in thousands, except per share data):

	Year Ended May 31,
	2018		2017		2016
Stock-based compensation in the form of stock options, RSUs, and ESPP purchase rights, included in:
Cost of sales	$	148	$	91	$	87
Selling, general and administrative		592		714		723
Research and development		256		194		206
Net effect on net income (loss)	$	996	$	999	$	1,016
Effect on net income (loss) per share:
Basic	$	0.05	$	0.06	$	0.08
Diluted	$	0.04	$	0.06	$	0.08

Fair value assumptions for Option Valuation Model

The fair values of the Company’s stock options granted to employees in fiscal 2018, 2017 and 2016 were estimated using the following weighted average assumptions in the Black-Scholes option valuation method:

	Year Ended May 31,
	2018			2017			2016
Option plan shares
Expected term (in years)		4			4			4
Volatility		0.77			0.81			0.86
Risk-free interest rates		1.95	%		1.02	%		1.21	%
Weighted-average grant date fair value	$	2.07		$	1.09		$	1.31

Fair value assumption of the ESPP Purchase Rights

    The fair value of our ESPP purchase rights for the fiscal 2018, 2017 and 2016 was estimated using the following weighted-average assumptions:

	Year End May 31,
	2018	2017	2016
Employee stock purchase plan shares
Expected term (in years)	0.5 – 2.0	0.5 – 2.0	0.5 – 2.0
Volatility	0.56 – 0.81	0.79 – 1.08	0.64 – 0.74
Risk-free interest rates	1.92%–2.25%	0.48%–0.80%	0.40%–0.76%
Weighted-average grant date fair value	$1.01	$1.65	$0.80

Stock option and RSU transactions

    The following tables summarize the Company’s stock option and RSU transactions during fiscal 2018, 2017 and 2016 (in thousands):

	Available
	Shares
Balances, May 31, 2015		845
Additional shares reserved		800
Options granted		(92	)
RSUs granted		(35	)
Options terminated		329
Balances, May 31, 2016		1,847
Additional shares reserved		2,238
Options granted		(368	)
RSUs granted		(157	)
Options terminated		55
Plan shares expired		(1,446	)
Balances, May 31, 2017		2,169
Options granted		(338	)
RSUs granted		(64	)
RSUs cancelled		33
Options terminated		16
Plan shares expired		(4	)
Balances, May 31, 2018		1,812

Stock option transactions

    The following table summarized the stock option transactions during fiscal 2018, 2017 and 2016 (in thousands, except per share data):

	Outstanding Options
				Weighted
	Number			Average		Aggregate
	of			Exercise		Intrinsic
	Shares			Price		Value
Balances, May 31, 2015		3,686		$	1.66	$	2,946
Options granted		92		$	2.12
Options terminated		(329	)	$	1.93
Options exercised		(248	)	$	1.34
Balances, May 31, 2016		3,201		$	1.66	$	189
Options granted		368		$	1.83
Options terminated		(55	)	$	1.42
Options exercised		(440	)	$	1.35
Balances, May 31, 2017		3,074		$	1.73	$	8,763
Options granted		338		$	3.56
Options terminated		(16	)	$	2.72
Options exercised		(537	)	$	1.17
Balances, May 31, 2018		2,859		$	2.04	$	1,987
Options fully vested and expected to vest at May 31, 2018		2,825		$	2.04	$	1,976

Options outstanding

    The options outstanding and exercisable at May 31, 2018 were in the following exercise price ranges (in thousands, except per share data):

		Options Outstanding						Options Exercisable
		at May 31, 2018						at May 31, 2018
Range of Exercise Prices		Number Outstanding Shares		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable Shares		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Aggregate Intrinsic Value
$	0.59-$0.97		299		0.77	$	0.67		299		0.77	$	0.67
$	1.09-$1.36		557		1.64	$	1.28		556		1.64	$	1.28
$	1.68-$2.06		483		4.23	$	1.74		314		3.73	$	1.78
$	2.10-$2.81		1,257		3.68	$	2.45		1,073		3.49	$	2.47
$	3.46-$3.93		263		6.16	$	3.86		70		6.21	$	3.77
$	0.59-$3.93		2,859		3.30	$	2.04		2,312		2.81	$	1.89	$	1,778