Acquisitions (Recognized Amounts Of Identifiable Assets Acquired And Liabilities) (Details) (USD $) In Thousands, unless otherwise specified				0 Months Ended				0 Months Ended
	Mar. 31, 2012	Aug. 01, 2011	Aug. 01, 2011 Apache Design Solutions, Inc. [Member]	Aug. 01, 2011 Apache Design Solutions, Inc. [Member] Developed Software [Member] Y	Aug. 01, 2011 Apache Design Solutions, Inc. [Member] Customer Relationships [Member] Y	Aug. 01, 2011 Apache Design Solutions, Inc. [Member] Contract Backlog [Member] Y	Aug. 01, 2011 Apache Design Solutions, Inc. [Member] Platform Trade Names [Member]	Aug. 01, 2011 Apache Design Solutions, Inc. [Member] Apache Trade Name [Member] Y
Business Acquisition [Line Items]
Cash and short-term investments			$ 31,948
Accounts receivable and other tangible assets			6,011
Amortizable intangible assets	154,000	151,700		82,500	36,100	13,500		2,100
Indefinite-lived intangible assets							21,900
Accounts payable and other liabilities			(16,038)
Deferred revenue	(10,100)		(10,100)
Net deferred tax liabilities	48,800	46,100	(48,833)
Total identifiable net assets			119,088
Goodwill			$ 194,889
Useful life of intangible assets acquired, in years				7	15	3		6