| Document and Entity Information | Dec. 02, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | Coupa Software Inc |
| Amendment Flag | false |
| Entity Central Index Key | 0001385867 |
| Document Type | 8-K |
| Document Period End Date | Dec. 2, 2019 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-37901 |
| Entity Tax Identification Number | 20-4429448 |
| Entity Address, Address Line One | 1855 S. Grant Street |
| Entity Address, City or Town | San Mateo |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94402 |
| City Area Code | 650 |
| Local Phone Number | 931-3200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | COUP |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
