Taxes (Narrative) (Details) (USD $)	3 Months Ended			9 Months Ended	3 Months Ended
	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2010	Jul. 31, 2011	Jan. 31, 2010 Increase Net [Member]	Jan. 31, 2010 Avant! Corporation [Member]	Jan. 31, 2011 Synplicity, Inc. [Member]
Statutory federal income tax rate	35.00%
Tax impact of final settlement with IRS		$ 32,800,000				$ 94,300,000
Estimated potential decrease in underlying unrecognized tax benefits, minimum	0			0
Estimated potential decrease in underlying unrecognized tax benefits, maximum	85,000,000			85,000,000
Decrease in unrecognized tax benefits resulting from settlement with the IRS		35,900,000				67,800,000	4,000,000
Valuation allowance						21,600,000
Decrease in deferred tax assets due to foreign tax credit carryover			(25,200,000)
Income tax examination years		IRS for its audits of fiscal years 2006 through 2009	audit of its fiscal years 2002 through 2004	IRS for its audits of fiscal years 2006 through 2009	audit of its fiscal years 2002 through 2004	audit of its fiscal years 2002 through 2004
Non-US Examinations	0			0
Tax adjustments settlements and unusual provisions			$ 72,300,000		$ 55,400,000