Share-Based Compensation (Details) - USD ($) $ in Thousands			3 Months Ended		6 Months Ended
		Apr. 04, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation expense [Line Items]
Allocated share-based compensation expense			$ 23,610	$ 24,390	$ 46,018	$ 83,969
Income tax benefit			7,846	8,358	15,274	29,246
Net income effect of share-based compensation			15,764	16,032	30,744	54,723
Share-based compensation expense previously capitalized			3,700		7,100
Inventory
Stock-based compensation expense [Line Items]
Income tax benefit			3,100	2,700	5,800	5,500
Share-based compensation expense previously capitalized				4,100		7,800
Cost of Sales
Stock-based compensation expense [Line Items]
Allocated share-based compensation expense			3,699	4,100	7,093	11,997
Research and development
Stock-based compensation expense [Line Items]
Allocated share-based compensation expense			10,587	10,171	20,876	27,688
Selling, General and Administrative
Stock-based compensation expense [Line Items]
Allocated share-based compensation expense			9,324	10,119	18,049	44,284
Atmel Corporation
Stock-based compensation expense [Line Items]
Allocated share-based compensation expense	[1]		6,200		49,400
Share-based compensation expense previously capitalized						4,200
Non cash consideration of certain share-based payment awards		$ 7,500
Accelerated compensation cost					37,200
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2016-09, Excess Tax Benefit Component
Stock-based compensation expense [Line Items]
Allocated share-based compensation expense			$ 8,200	$ 5,800	$ 14,100	$ 12,500

[1] During the three and six months ended September 30, 2017, $3.1 million and $5.8 million, respectively, of share-based compensation expense was capitalized to inventory and $3.7 million and $7.1 million, respectively, of previously capitalized share-based compensation expense in inventory was sold. During the three and six months ended September 30, 2016, $2.7 million and $5.5 million, respectively, of share-based compensation expense was capitalized to inventory. The amount of share-based compensation included in cost of sales during the three months ended September 30, 2016 included $4.1 million of previously capitalized share-based compensation expense in inventory that was sold. The amount of share-based compensation included in cost of sales during the six months ended September 30, 2016 included $7.8 million of previously capitalized share-based compensation expense in inventory that was sold and $4.2 million of share-based compensation expense related to the Company's acquisition of Atmel that was not previously capitalized to inventory.