Equity Incentive Plans, Stock Compensation Expensed (Details) (USD $)	12 Months Ended					12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2013 SMSC Acquisition [Member] Equity awards assumed in acquisition [Member]	Aug. 01, 2012 SMSC Acquisition [Member] Equity awards assumed in acquisition [Member]	Mar. 31, 2013 Inventory [Member]	Mar. 31, 2012 Inventory [Member]	Mar. 31, 2011 Inventory [Member]	Mar. 31, 2013 Cost of sales [Member]		Mar. 31, 2012 Cost of sales [Member]		Mar. 31, 2011 Cost of sales [Member]		Mar. 31, 2013 Research and development [Member]	Mar. 31, 2012 Research and development [Member]	Mar. 31, 2011 Research and development [Member]	Mar. 31, 2013 Selling, general and administrative [Member]	Mar. 31, 2012 Selling, general and administrative [Member]	Mar. 31, 2011 Selling, general and administrative [Member]	Mar. 31, 2013 Pre-tax effect of share based compensation [Member]	Mar. 31, 2012 Pre-tax effect of share based compensation [Member]	Mar. 31, 2011 Pre-tax effect of share based compensation [Member]	Mar. 31, 2013 Income tax benefit [Member]	Mar. 31, 2012 Income tax benefit [Member]	Mar. 31, 2011 Income tax benefit [Member]
Stock-based compensation expense [Line Items]
Allocated share based compensation expense	$ 48,977,000	$ 33,400,000	$ 32,319,000						$ 8,234,000	[1]	$ 5,648,000	[1]	$ 6,825,000	[1]	$ 22,178,000	$ 14,719,000	$ 12,874,000	$ 27,603,000	$ 17,922,000	$ 17,113,000	$ 58,015,000	$ 38,289,000	$ 36,812,000	$ 9,038,000	$ 4,889,000	$ 4,493,000
Amount of share-based compensation expense capitalized to inventory						5,900,000	6,600,000	7,100,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	87,500,000				21,300,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2 years 2 months 8 days
Share Based Compensation Due to Accelerated Vesting				7,800,000
Total Fair Value of Assumed Awards Due to Acquisition					28,200,000
Business Acquisition, Cost of Acquired Entity, Equity Interests Issued and Issuable					$ 6,900,000

[1] During the year ended March 31, 2013, $5.9 million of share-based compensation expense was capitalized to inventory, and $8.2 million of previously capitalized share-based compensation expenses in inventory was sold. During the year ended March 31, 2012, $6.6 million of share-based compensation expense was capitalized to inventory, and $5.6 million of previously capitalized share-based compensation expense in inventory was sold. During the year ended March 31, 2011, $7.1 million of share-based compensation expense was capitalized to inventory, and $6.8 million of previously capitalized share-based compensation expense in inventory was sold.