Intangible Assets, by Major Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 2,706,512	$ 1,075,013
Accumulated Amortization	(558,420)	(468,664)
Net Amount	2,148,092	606,349
In-process technology reaching technological feasibility and reclassified	156,700
Projected Amortization Expense
2018	490,382
2019	361,988
2020	313,288
2021	256,930
2022	189,881
Amortization of acquired intangible assets	346,300	179,300	$ 181,000
Impairment of intangible assets	11,904	629	1,881
Cost of Sales
Projected Amortization Expense
Amortization of acquired intangible assets	4,000	3,600	3,800
Operating Expense
Projected Amortization Expense
Amortization of acquired intangible assets	$ 342,300	175,700	$ 177,200
Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life (in years)	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life (in years)	15 years
Core and developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 1,932,329	724,883
Accumulated Amortization	(419,468)	(255,460)
Net Amount	1,512,861	469,423
Purchased intangible assets	$ 1,215,700
Acquired finite-lived intangible assets, weighted average useful life (in years)	11 years
Customer-related
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 716,945	278,542
Accumulated Amortization	(123,616)	(200,331)
Net Amount	593,329	78,211
Purchased intangible assets	$ 630,600
Acquired finite-lived intangible assets, weighted average useful life (in years)	6 years
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 11,700	11,700
Accumulated Amortization	(9,636)	(7,571)
Net Amount	2,064	4,129
Backlog
Finite-Lived Intangible Assets [Line Items]
Purchased intangible assets	$ 40,300
Acquired finite-lived intangible assets, weighted average useful life (in years)	1 year
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Purchased intangible assets	$ 1,800
Acquired finite-lived intangible assets, weighted average useful life (in years)	5 years
In-process research and development
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 38,511	54,308
Accumulated Amortization	0	0
Net Amount	38,511	54,308
Distribution rights
Finite-Lived Intangible Assets [Line Items]
Gross Amount	5,578	5,580
Accumulated Amortization	(5,346)	(5,302)
Net Amount	232	$ 278
Other
Finite-Lived Intangible Assets [Line Items]
Gross Amount	1,449
Accumulated Amortization	(354)
Net Amount	$ 1,095