STOCK PLANS AND STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation Expense Included in Statements of Operations

The following table summarizes the amount of stock-based compensation expense included in the consolidated statements of operations for the periods presented:

	Fiscal Year Ended March 31,
(in thousands)	2016			2017			2018
Cost of revenues	$	3,306		$	3,244		$	3,622
Research, development and engineering	9,908			8,616			8,071
Selling, general and administrative	20,051			21,679			22,266
Stock-based compensation expense included in operating expenses	29,959			30,295			30,337
Total stock-based compensation	33,265			33,539			33,959
Income tax benefit	(10,950		)	(10,768		)	(7,880		)
Total stock-based compensation expense, net of tax	$	22,315		$	22,771		$	26,079

Summary of Stock Option Activity

The following is a summary of the Company’s stock option activity during Fiscal Year 2018:

	Options Outstanding
	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)				(in years)	(in thousands)
Outstanding at March 31, 2017	1,417		$	43.41
Options granted	15		$	52.11
Options exercised	(505	)	$	36.04
Options forfeited or expired	(4	)	$	53.23
Outstanding at March 31, 2018	923		$	47.53	3.8	$	11,853
Vested or expected to vest at March 31, 2018	918		$	47.54	3.8	$	11,781
Exercisable at March 31, 2018	758		$	47.69	3.5	$	9,612

Summary of Restricted Stock Activity

The following is a summary of the Company’s restricted stock activity during Fiscal Year 2018:

	Number of Shares		Weighted Average Grant Date Fair Value
	(in thousands)
Unvested at March 31, 2017	1,172		$	47.86
Restricted stock granted	784		$	53.62
Restricted stock vested	(577	)	$	48.12
Restricted stock forfeited	(125	)	$	50.30
Non-vested at March 31, 2018	1,254		$	51.09

Valuation Assumptions

The Company estimates the fair value of stock options and ESPP shares using a Black-Scholes option valuation model.  At the date of grant, the Company estimated the fair value of each stock option grant and purchase right granted under the ESPP using the following weighted average assumptions:

	Employee Stock Options									ESPP
Fiscal Year Ended March 31,	2016			2017			2018			2016			2017			2018
Expected volatility	27.0		%	31.1		%	29.1		%	33.5		%	28.8		%	30.5		%
Risk-free interest rate	1.4		%	1.1		%	1.7		%	0.3		%	0.6		%	1.5		%
Expected dividends	1.1		%	1.4		%	1.2		%	1.4		%	1.1		%	1.2		%
Expected life (in years)	4.2			4.4			4.6			0.5			0.5			0.5
Weighted-average grant date fair value	$	11.39		$	10.39		$	12.58		$	10.33		$	12.03		$	11.78