STOCK PLANS AND STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Mar. 31, 2017

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)	2015			2016			2017
Cost of revenues	$	2,583		$	3,306		$	3,244
Research, development and engineering	8,053			9,908			8,616
Selling, general and administrative	17,958			20,051			21,679
Stock-based compensation expense included in operating expenses	26,011			29,959			30,295
Total stock-based compensation	28,594			33,265			33,539
Income tax benefit	(8,451		)	(10,950		)	(10,768		)
Total stock-based compensation expense, net of tax	$	20,143		$	22,315		$	22,771

Summary of Stock Option Activity

The following is a summary of the Company’s stock option activity during Fiscal Year 2017:

	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, 2016	1,461		$	41.24
Options granted	251		$	44.00
Options exercised	(295	)	$	33.20
Options forfeited or expired	—		$	—
Outstanding at March 31, 2017	1,417		$	43.41	4.0	$	15,209
Vested or expected to vest at March 31, 2017	1,393		$	43.35	3.9	$	15,030
Exercisable at March 31, 2017	1,007		$	41.80	3.2	$	12,415

Summary of Restricted Stock Activity

The following is a summary of the Company’s restricted stock activity during Fiscal Year 2017:

	Number of Shares		Weighted Average Grant Date Fair Value
	(in thousands)
Unvested at March 31, 2016	1,187		$	48.95
Restricted stock granted	673		$	44.82
Restricted stock vested	(620	)	$	46.57
Restricted stock forfeited	(68	)	$	48.52
Non-vested at March 31, 2017	1,172		$	47.86

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,	2015			2016			2017			2015			2016			2017
Expected volatility	28.4		%	27.0		%	31.1		%	25.5		%	33.5		%	28.8		%
Risk-free interest rate	1.4		%	1.4		%	1.1		%	0.1		%	0.3		%	0.6		%
Expected dividends	1.3		%	1.1		%	1.4		%	1.2		%	1.4		%	1.1		%
Expected life (in years)	4.2			4.2			4.4			0.5			0.5			0.5
Weighted-average grant date fair value	$	10.33		$	11.39		$	10.39		$	10.57		$	10.33		$	12.03