Stock-Based Compensation (Assumptions To Estimate Fair Value Of Stock Awards) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016 $ / shares	Dec. 31, 2015 $ / shares
Stock Option Compensation Expense [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.00%	1.19%	1.18%
Risk-free interest rate, maximum	0.00%	1.93%	1.65%
Expected dividend yield		0.00%	0.00%
Expected volatility		24.00%	25.00%
Expected term (in years)		5 years 8 months 7 days	5 years 7 months 7 days
Weighted-average fair value per share		$ 23.96	$ 30.83
Restricted Stock Unit Compensation Expense [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	2 years 9 months 18 days	2 years 9 months 18 days	2 years 9 months 18 days
Risk-free interest rate	1.50%	1.00%	1.10%
Correlation factor	0.70	0.65	0.60
Restricted Stock Unit Compensation Expense [Member] \| ANSYS Stock Price [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility	19.00%	21.00%	23.00%
Restricted Stock Unit Compensation Expense [Member] \| NASDAQ Composite Index [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility	15.00%	16.00%	14.00%

Share-based compensation arrangement by share-based payment award, fair value assumptions, correlation factor

No definition available.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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No definition available.

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- Definition

The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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