Special Charges (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended
	Mar. 31, 2013 Unusual or Infrequent Item [Member]	Mar. 31, 2012 Unusual or Infrequent Item [Member]	Mar. 31, 2013 SMSC Acquisition [Member] Unusual or Infrequent Item [Member]	Sep. 30, 2012 SST acquisition [Member] Unusual or Infrequent Item [Member]	Mar. 31, 2013 SST acquisition [Member] Unusual or Infrequent Item [Member]	Mar. 31, 2011 SST acquisition [Member] Unusual or Infrequent Item [Member]	Mar. 31, 2013 Roving Networks Acquisition [Member]	Mar. 31, 2013 Roving Networks Acquisition [Member] Unusual or Infrequent Item [Member]
Unusual or Infrequent Item [Line Items]
Other Nonrecurring Expense	$ 32,200,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability		(1,000,000)					4,400,000	4,400,000
Severance related, office closing and other costs			16,300,000			1,900,000
Legal settlement costs				11,500,000	11,500,000
Other Nonrecurring Income		700,000
Severance Costs		300,000
Total Payment for Patent License Settlement		2,800,000
Patent License Expense Charged to Operations		1,500,000
Patent License Settlement Recorded as Prepaid Royalty		$ 1,300,000