Intangible Assets, by Major Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 1,075,013	$ 898,086
Accumulated Amortization	(468,664)	(393,669)
Net Amount	606,349	504,417
In-process technology reaching technological feasibility and reclassified	33,800
Projected Amortization Expense
2017	137,321
2018	110,811
2019	94,573
2020	76,683
2021	50,974
Amortization of acquired intangible assets	179,300	181,000	$ 99,400
Impairment of intangible assets	629	1,881	350
Cost of sales
Projected Amortization Expense
Amortization of acquired intangible assets	3,600	3,800	4,700
Operating Expense
Projected Amortization Expense
Amortization of acquired intangible assets	$ 175,700	177,200	$ 94,700
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	15 years
Core and developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 724,883	549,415
Accumulated Amortization	(255,460)	(189,149)
Net Amount	469,423	360,266
Acquired Finite-lived Intangible Asset, Amount	$ 175,800
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Customer-related
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 278,542	262,769
Accumulated Amortization	(200,331)	(192,283)
Net Amount	78,211	70,486
Acquired Finite-lived Intangible Asset, Amount	$ 71,100
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 11,700	13,180
Accumulated Amortization	(7,571)	(6,979)
Net Amount	4,129	6,201
Backlog
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Amount	$ 5,600
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	1 year
In-process technology
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 54,308	67,142
Accumulated Amortization	0	0
Net Amount	54,308	67,142
Acquired Finite-lived Intangible Asset, Amount	$ 21,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Distribution rights
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 5,580	5,580
Accumulated Amortization	(5,302)	(5,258)
Net Amount	$ 278	$ 322