STOCK PLANS AND STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Mar. 31, 2016

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)	2014			2015			2016
Cost of revenues	$	2,554		$	2,583		$	3,306
Research, development and engineering	6,404			8,053			9,908
Selling, general and administrative	14,222			17,958			20,051
Stock-based compensation expense included in operating expenses	20,626			26,011			29,959
Total stock-based compensation	23,180			28,594			33,265
Income tax benefit	(6,790		)	(8,451		)	(10,950		)
Total stock-based compensation expense, net of tax	$	16,390		$	20,143		$	22,315

Summary of Stock Option Activity

The following is a summary of the Company’s stock option activity during fiscal year 2016:

	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, 2015	1,558		$	36.59
Options granted	287		$	53.55
Options exercised	(329	)	$	28.80
Options forfeited or expired	(55	)	$	48.00
Outstanding at March 31, 2016	1,461		$	41.24	3.8	$	4,342
Vested or expected to vest at March 31, 2016	1,431		$	41.02	3.8	$	4,342
Exercisable at March 31, 2016	1,038		$	37.15	3.0	$	4,334

Summary of Restricted Stock Activity

The following is a summary of the Company’s restricted stock activity during fiscal year 2016:

	Number of Shares		Weighted Average Grant Date Fair Value
	(in thousands)
Non-vested at March 31, 2015	1,290		$	42.67
Restricted stock granted	668		$	54.66
Restricted stock vested	(579	)	$	41.86
Restricted stock forfeited	(192	)	$	48.05
Non-vested at March 31, 2016	1,187		$	48.95

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,	2014			2015			2016			2014			2015			2016
Expected volatility	32.2		%	28.4		%	27.0		%	26.5		%	25.5		%	33.5		%
Risk-free interest rate	0.9		%	1.4		%	1.4		%	0.1		%	0.1		%	0.3		%
Expected dividends	0.9		%	1.3		%	1.1		%	0.9		%	1.2		%	1.4		%
Expected life (in years)	4.2			4.2			4.2			0.5			0.5			0.5
Weighted-average grant date fair value	$	11.15		$	10.33		$	11.39		$	9.62		$	10.57		$	10.33