Stock Award Plans and Stock-Based Compensation (Tables)

12 Months Ended

Mar. 31, 2017

Stock-Based Compensation Recognized

The following table summarizes stock-based compensation expense by financial statement line item in the Company’s consolidated statements of operations for the fiscal years ended March 31, 2017, 2016 and 2015:

	Fiscal Years Ended March 31,
		2017		2016		2015
	(in $000's)
Cost of product revenue	$	1,061	$	895	$	665
Research and development		6,050		3,950		3,205
Selling, general and administrative		25,755		24,208		12,650
	$	32,866	$	29,053	$	16,520

Components of Stock-Based Compensation

The components of stock-based compensation for the fiscal years ended March 31, 2017, 2016 and 2015 were as follows:

	Fiscal Years Ended March 31,
		2017		2016		2015
	(in $000's)
Restricted stock units	$	26,570	$	23,708	$	13,539
Stock options		5,829		4,866		2,708
Employee stock purchase plan		467		479		273
	$	32,866	$	29,053	$	16,520

Summary of Stock Option Activity

The following table summarized stock option activity for the year ended March 31, 2017:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
	Options			Exercise		Contractual		Value
	(in thousands)			Price		Term (years)		(in thousands)
Outstanding at beginning of period		2,244		$	20.55		5.19
Granted		180			106.10
Exercised		(755	)		14.12
Cancelled and expired		(23	)		73.50
Outstanding at end of period		1,646		$	32.09		5.46	$	153,254
Exercisable at end of period		1,156		$	18.26		4.36	$	123,592
Options vested and expected to vest at end of period		1,594		$	31.06		5.37	$	150,056

Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted

The weighted average grant-date fair values and weighted average assumptions used in the calculation of fair value of options granted during the fiscal years ended March 31, 2017, 2016 and 2015 was as follows:

	Fiscal Years Ended March 31,
		2017			2016			2015
Valuation assumptions:
Weighted average grant-date fair value	$	42.40		$	29.57		$	9.29
Risk-free interest rate		1.41	%		1.55	%		1.60	%
Expected option life (years)		4.14			4.15			4.19
Expected volatility		48.9	%		49.7	%		49.3	%

Restricted Stock Units

Summary of Restricted Stock Units Activity

The following table summarizes restricted stock unit activity for the fiscal year ended March 31, 2017:

	Number of Shares			Weighted Average Grant Date Fair Value
	(in thousands)			(per share)
Restricted stock units at beginning of period		1,263		$	57.95
Granted		366		$	97.43
Vested		(502	)	$	35.05
Forfeited		(71	)	$	91.39
Restricted stock units at end of period		1,056		$	80.50

Monte Carlo Simulation Model to Estimate Grant-Date Fair Value of Restricted Stock Units

The table below sets forth the assumptions used to value the market-based awards and the estimated grant-date fair value:

	June 2015 Awards			November 2016 Awards
Risk-free interest rate		1.10	%		0.90	%
Dividend yield		0	%		0	%
Remaining performance period (years)		1.21			1.21
Expected volatility		47.2	%		50.6	%
Estimated grant date fair value (per share)	$	107.10		$	62.55
Target performance (number of shares)		107,660			41,526