Acquisitions - Fair Value of Consideration Transferred 2020 (Details) - USD ($) shares in Thousands			12 Months Ended
	Dec. 01, 2020	Apr. 01, 2020	Dec. 31, 2020	Dec. 31, 2019
Cash			$ 597,342,000	$ 820,084,000
Ansys common stock			218,348,000	308,704,000
Consideration not yet paid			14,342,000
Total consideration transferred at fair value			830,032,000	$ 1,128,788,000
Analytical Graphics, Inc.
Cash	$ 489,797,000
Ansys common stock	218,348,000
Consideration not yet paid	14,342,000
Total consideration transferred at fair value	$ 722,487,000
Stock issued to prior owners of Analytical Graphics, Inc., amount			$ 218,348,000
Analytical Graphics, Inc. | Common Stock
Common stock issued to prior owners of Analytical Graphics, Inc., shares	600		638
Stock issued to prior owners of Analytical Graphics, Inc., amount	$ 217,400,000		$ 7,000
Analytical Graphics, Inc. | Treasury Stock
Stock issued to prior owners of Analytical Graphics, Inc., amount	$ 900,000		$ 233,000
Lumerical
Cash		$ 107,545,000
Total consideration transferred at fair value		$ 107,545,000