Document and Entity Information
| Document and Entity Information | Oct. 18, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | ALDER BIOPHARMACEUTICALS INC |
| Security Exchange Name | NASDAQ |
| Current Fiscal Year End Date | --12-31 |
| Amendment Flag | false |
| Entity Central Index Key | 0001423824 |
| Document Type | 8-K |
| Document Period End Date | Oct. 18, 2019 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36431 |
| Entity Tax Identification Number | 90-0134860 |
| Entity Address, Address Line One | 11804 North Creek Parkway South |
| Entity Address, City or Town | Bothell |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98011 |
| City Area Code | 425 |
| Local Phone Number | 205-2900 |
| 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 | ALDR |
| Entity Emerging Growth Company | false |