| Document And Entity Information | Dec. 16, 2020 |
| Document Information Line Items | |
| Entity Registrant Name | General Finance Corporation |
| Document Type | 8-K |
| Amendment Flag | false |
| Entity Central Index Key | 0001342287 |
| Document Period End Date | Dec. 16, 2020 |
| Entity Emerging Growth Company | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-32845 |
| Entity Tax Identification Number | 32-0163571 |
| Entity Address, Address Line One | 39 East Union Street |
| Entity Address, City or Town | Pasadena |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 91103 |
| City Area Code | 626 |
| Local Phone Number | 584-9722 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Common Stock [Member] | |
| Document Information Line Items | |
| Trading Symbol | GFN |
| Title of 12(b) Security | Common Stock, $0.0001 par value |
| Security Exchange Name | NASDAQ |
| Preferred Stock [Member] | |
| Document Information Line Items | |
| Trading Symbol | GFNCP |
| Title of 12(b) Security | 9.00% Series C Cumulative Redeemable Perpetual Preferred Stock (Liquidation Preference $100 per share) |
| Security Exchange Name | NASDAQ |
| Senior Note Due 2021 [Member] | |
| Document Information Line Items | |
| Trading Symbol | GFNSL |
| Title of 12(b) Security | 8.125% Senior Notes due 2021 |
| Security Exchange Name | NASDAQ |
| Senior Note Due 2025 [Member] | |
| Document Information Line Items | |
| Trading Symbol | GFNSZ |
| Title of 12(b) Security | 7.875% Senior Notes due 2025 |
| Security Exchange Name | NASDAQ |
