Acquisitions (Narrative) (Details) (USD $)	7 Months Ended	12 Months Ended	5 Months Ended	12 Months Ended
	Aug. 01, 2011 years	Dec. 31, 2011	Dec. 31, 2011 Apache Design Solutions, Inc. [Member]	Dec. 31, 2011 Apache Design Solutions, Inc. [Member]	Aug. 01, 2011 Apache Design Solutions, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, acquisition percentage					100.00%
Business acquisition, purchase price					$ 313,977,000
Business acquisition, cash on subsidiary balance sheet			31,948,000	31,948,000
ANSYS replacement stock options					3,170,000
Business combination, goodwill recognized, description		The goodwill, which is not tax-deductible, is attributed to intangible assets that do not qualify for separate recognition, including the assembled workforce of the acquired business and the synergies expected to arise as a result of the acquisition of Apache.
Contingent consideration			9,600,000	9,600,000	(9,501,000)
Business acquisition, incentive and provision fiscal period (in years)	3
Business acquisition, potential performance equity awards			13,000,000	13,000,000
Revenues of acquired business			14,500,000
Net loss from acquired business			4,200,000
Acquisition-related costs		2,100,000
Contingent consideration arrangement, additional payments					12,000,000
Acquired deferred revenue			10,100,000	10,100,000
Acquired deferred revenue, amount lower than the historical carrying value recorded on the opening balance sheet			13,600,000	13,600,000
Acquired deferred revenue, impact on reported revenue				9,600,000
Acquired deferred revenue, expected impact on reported revenue in next fiscal year				3,400,000
Increase in of identifiable intangible assets during measurement period		2,300,000
Reduction in values of net deferred tax liabilities during measurement period		1,900,000
Reduction in values of goodwill during measurement period		$ 4,300,000
Nature of preliminary adjustments		These adjustments were based on refinements to assumptions used in the preliminary valuation of intangible assets and new information obtained in the calculation of the net deferred tax liabilities.