| Document and Entity Information | Nov. 03, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 3, 2020 |
| Entity Registrant Name | HILLS BANCORPORATION |
| Entity Incorporation, State or Country Code | IA |
| Entity File Number | 0-12668 |
| Entity Tax Identification Number | 42-1208067 |
| Entity Address, Address Line One | 131 E. Main Street, PO Box 160 |
| Entity Address, City or Town | Hills |
| Entity Address, State or Province | IA |
| Entity Address, Postal Zip Code | 52235 |
| City Area Code | 319 |
| Local Phone Number | 679-2291 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000732417 |
| Amendment Flag | false |
