Goodwill by Reporting Segment (Details) (USD $) In Thousands, unless otherwise specified					6 Months Ended					6 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2012 Semiconductor products [Member]	Mar. 31, 2012 Semiconductor products [Member]	Sep. 30, 2012 Semiconductor products [Member] SMSC Acquisition [Member]	Sep. 30, 2012 Semiconductor products [Member] Roving Networks Acquisition [Member]	Sep. 30, 2012 Semiconductor products [Member] Acquisition Of R And E International Member	Sep. 30, 2012 Technology licensing [Member]	Mar. 31, 2012 Technology licensing [Member]	Sep. 30, 2012 Technology licensing [Member] SMSC Acquisition [Member]	Sep. 30, 2012 Technology licensing [Member] Roving Networks Acquisition [Member]	Sep. 30, 2012 Technology licensing [Member] Acquisition Of R And E International Member
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 260,059	$ 93,513	$ 240,859	$ 74,313				$ 19,200	$ 19,200
Additions due to business combination					157,840	8,652	54			0	0	0
Goodwill, ending balance	$ 260,059	$ 93,513	$ 240,859	$ 74,313				$ 19,200	$ 19,200