| Document and Entity Information | Feb. 25, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001347178 |
| Document Type | 8-K |
| Document Period End Date | Feb. 25, 2020 |
| Entity Registrant Name | VANDA PHARMACEUTICALS INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-34186 |
| Entity Tax Identification Number | 03-0491827 |
| Entity Address, Address Line One | 2200 Pennsylvania Avenue NW |
| Entity Address, Address Line Two | Suite 300E |
| Entity Address, City or Town | Washington |
| Entity Address, State or Province | DC |
| Entity Address, Postal Zip Code | 20037 |
| City Area Code | (202) |
| Local Phone Number | 734-3400 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.001 per share |
| Trading Symbol | VNDA |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
