Stock-Based Compensation Expense and Its Net Impact on Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Service Share-Based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense before taxes	$ 8,952	$ 8,870	$ 24,564	$ 25,731
Related income tax benefits	(2,993)	(2,725)	(7,928)	(8,454)
Stock-based compensation expense, net of taxes	$ 5,959	$ 6,145	$ 16,636	$ 17,277
Basic earnings per share	$ (0.07)	$ (0.07)	$ (0.19)	$ (0.19)
Diluted earnings per share	$ (0.07)	$ (0.07)	$ (0.19)	$ (0.19)
Software Licenses
Employee Service Share-Based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense before taxes	$ 187	$ 174	$ 524	$ 549
Maintenance and Service
Employee Service Share-Based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense before taxes	417	530	1,200	1,432
Selling, General and Administrative
Employee Service Share-Based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense before taxes	4,292	4,249	11,160	13,038
Research and Development
Employee Service Share-Based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense before taxes	$ 4,056	$ 3,917	$ 11,680	$ 10,712

Reduction in Basic Earnings per Share Impact of Stock Based Compensation

No definition available.

Name:	anss_ReductionInBasicEarningsPerShareImpactOfStockBasedCompensation
Namespace Prefix:	anss_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Reduction in Diluted Earnings per Share Impact of Stock Based Compensation

+ References

No definition available.

+ Details

Name:	anss_ReductionInDilutedEarningsPerShareImpactOfStockBasedCompensation
Namespace Prefix:	anss_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

No definition available.

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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.

+ References

No definition available.

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

+ Details

Name:	us-gaap_ShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_IncomeStatementLocationAxis=anss_SoftwareLicensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=anss_MaintenanceAndServiceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_GeneralAndAdministrativeExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_ResearchAndDevelopmentExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: