| Cover | May 04, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | May 04, 2023 |
| Entity File Number | 001-37924 |
| Entity Registrant Name | BLACKLINE, INC. |
| Entity Central Index Key | 0001666134 |
| Entity Tax Identification Number | 46-3354276 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 21300 Victory Boulevard, 12th Floor |
| Entity Address, City or Town | Woodland Hills |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 91367 |
| City Area Code | 818 |
| Local Phone Number | 223-9008 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | BL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
