STOCK-BASED COMPENSATION (Tables)

6 Months Ended

Sep. 30, 2015

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 included in the condensed consolidated statements of operations:

	Three Months Ended   September 30,						Six Months Ended   September 30,
(in thousands)	2014			2015			2014			2015
Cost of revenues	$	668		$	879		$	1,203		$	1,658
Research, development and engineering	2,115			2,619			3,866			4,978
Selling, general and administrative	4,604			5,334			8,623			10,246
Stock-based compensation included in operating expenses	6,719			7,953			12,489			15,224
Total stock-based compensation	7,387			8,832			13,692			16,882
Income tax benefit	(2,239		)	(2,642		)	(4,028		)	(4,964		)
Total stock-based compensation, net of tax	$	5,148		$	6,190		$	9,664		$	11,918

Summary of Stock Option Activity

The following is a summary of the Company’s stock option activity during the six months ended September 30, 2015:

	Options Outstanding
	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
	(in thousands)		(in dollars)		(in years)	(in thousands)
Outstanding at March 31, 2015	1,558		$	36.59
Options granted	156		$	54.17
Options exercised	(197	)	$	30.98
Options forfeited or expired	(36	)	$	46.67
Outstanding at September 30, 2015	1,481		$	38.95	4.0	$	18,645
Vested or expected to vest at September 30, 2015	1,448		$	38.68	3.9	$	18,580
Exercisable at September 30, 2015	1,032		$	34.39	3.1	$	17,315

Summary of Restricted Stock Activity

Restricted stock consists of awards of restricted stock and restricted stock units ("RSUs"). The following is a summary of the Company’s restricted stock activity during the six months ended September 30, 2015:

	Number of Shares		Weighted Average Grant Date Fair Value
	(in thousands)
Non-vested at March 31, 2015	1,290		$	42.67
Restricted stock granted	643		$	55.04
Restricted stock vested	(546	)	$	41.76
Restricted stock forfeited	(49	)	$	46.01
Non-vested at September 30, 2015	1,338		$	48.86

Valuation Assumptions

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:

	Three Months Ended   September 30,						Six Months Ended   September 30,
Employee Stock Options	2014(1)			2015			2014			2015
Expected volatility	n/a			26.7		%	28.4		%	27.2		%
Risk-free interest rate	n/a			1.4		%	1.4		%	1.3		%
Expected dividend yield	n/a			1.1		%	1.4		%	1.1		%
Expected life (in years)	n/a			4.2			4.2			4.2
Weighted-average grant date fair value	n/a			$	12.02		$	9.21		$	11.54
ESPP
Expected volatility	24.8		%	21.9		%	24.8		%	21.9		%
Risk-free interest rate	0.1		%	0.3		%	0.1		%	0.3		%
Expected dividend yield	1.3		%	1.1		%	1.3		%	1.1		%
Expected life (in years)	0.5			0.5			0.5			0.5
Weighted-average grant date fair value	$	10.13		$	11.73		$	10.13		$	11.73

⁽¹⁾ No employee stock options were granted during the three months ended September 30, 2014.