| Document And Entity Information | Nov. 08, 2021 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Hallador Energy Company |
| Document, Type | 8-K |
| Document, Period End Date | Nov. 8, 2021 |
| Entity, Incorporation, State or Country Code | CO |
| Entity, File Number | 001-34743 |
| Entity, Tax Identification Number | 84-1014610 |
| Entity, Address, Address Line One | 1183 East Canvasback Drive |
| Entity, Address, City or Town | Terre Haute |
| Entity, Address, State or Province | IN |
| Entity, Address, Postal Zip Code | 47802 |
| City Area Code | 812 |
| Local Phone Number | 299-2800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Shares |
| Trading Symbol | HNRG |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0000788965 |
