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Employee Stock Purchase Plan (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, number of shares authorized 39,800,000.0 39,800,000.0    
Share-based compensation arrangement by share-based payment award, expiration period   10 years    
Stock-based compensation expense   $ 33,347 $ 33,951 $ 36,861
Employee Stock | ANSYS 1996 Employee Stock Purchase Plan [Member]        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, number of shares authorized 1,800,000 1,800,000    
Share-based compensation arrangement by share-based payment award, expiration period   6 months    
Share-based compensation arrangement by share-based payment award, maximum employee subscription rate 10.00% 10.00%    
Maximum number of shares per employee   3,840    
Maximum employee subscription rate, value   $ 25    
Share-based compensation arrangement by share-based payment award, shares issued in period 1,400,000      
Stock-based compensation expense   $ 1,200 $ 1,000 $ 900
Maximum [Member] | Employee Stock | ANSYS 1996 Employee Stock Purchase Plan [Member]        
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]        
Eligibility, ownership percentage of voting power of all classes of stock of the company 5.00% 5.00%    
Purchase price of common stock, percent   90.00%