Business Combinations Business Combinations (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jul. 31, 2014	Jan. 31, 2014
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Mar. 20, 2014
Goodwill	$ 597,912	$ 549,044
Developed Technology Rights [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Business Combination, Recognized Identifiable Finite-Lived Intangibles	11,200
Other Intangible Assets [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Finite-Lived Intangibles	13,570
Other Intangible Assets [Member] | Minimum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Other Intangible Assets [Member] | Maximum
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Berkeley Design Automation, Inc.
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	46,832
Acquisition Related Deferred Payment	4,471
Business Combination, Consideration Transferred	51,303
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	2,335
Business Combination, Recognized Identifiable Finite-Lived Intangibles	24,770
Fair Value Inputs, Discount Rate	15.00%
Goodwill	24,198
Other Acquired Entities [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	39,094
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	1,606
Business Combination, Recognized Identifiable Finite-Lived Intangibles	12,540
Goodwill	24,948
Total FY15 Acquisitions [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	90,397
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	3,941
Business Combination, Recognized Identifiable Finite-Lived Intangibles	37,310
Goodwill	$ 49,146