| Cover | Mar. 29, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 29, 2023 |
| Entity Registrant Name | Appian Corporation |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-38098 |
| Entity Tax Identification Number | 54-1956084 |
| Entity Address, State or Province | VA |
| Entity Address, City or Town | McLean |
| Entity Address, Address Line One | 7950 Jones Branch Drive |
| Entity Address, Postal Zip Code | 22102 |
| City Area Code | 703 |
| Local Phone Number | 442-8844 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Common Stock |
| Trading Symbol | APPN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001441683 |
