Business Combinations Business Combinations (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Oct. 31, 2014	Jan. 31, 2014
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Mar. 20, 2014
Goodwill	$ 598,558	$ 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
Berkeley Design Automation, Inc.
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate	15.00%
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
Goodwill	24,198
Other Acquired Entities [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	42,165
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	827
Business Combination, Recognized Identifiable Finite-Lived Intangibles	13,440
Goodwill	27,898
Total FY15 Acquisitions [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	93,468
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	3,162
Business Combination, Recognized Identifiable Finite-Lived Intangibles	38,210
Goodwill	$ 52,096
Maximum | Other Intangible Assets [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Minimum | Other Intangible Assets [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years