| Document And Entity Information - USD ($) | Dec. 31, 2020 | Apr. 16, 2021 | Jun. 30, 2020 |
| Document Information [Line Items] | |||
| Entity, Registrant Name | Alaska Communications Systems Group, Inc. | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document, Fiscal Period Focus | FY | ||
| Document, Fiscal Year Focus | 2020 | ||
| Document, Type | 10-K/A | ||
| Document, Annual Report | true | ||
| Document, Period End Date | Dec. 31, 2020 | ||
| Document, Transition Report | false | ||
| Entity, File Number | 001-38341 | ||
| Entity, Incorporation, State or Country Code | DE | ||
| Entity, Tax Identification Number | 52-2126573 | ||
| Entity, Address, Address Line One | 600 Telephone Avenue | ||
| Entity, Address, Postal Zip Code | 99503-6091 | ||
| Entity, Address, City or Town | Anchorage | ||
| Entity, Address, State or Province | AK | ||
| City Area Code | 907 | ||
| Local Phone Number | 297-3000 | ||
| Title of 12(b) Security | Common Stock | ||
| Trading Symbol | ALSK | ||
| Security Exchange Name | NASDAQ | ||
| Entity, Well-known Seasoned Issuer | No | ||
| Entity, Voluntary Filers | No | ||
| Entity, Current Reporting Status | Yes | ||
| Entity, Interactive Data, Current | Yes | ||
| Entity, Filer Category | Accelerated Filer | ||
| Entity, Small Business | true | ||
| Entity, Emerging Growth Company | false | ||
| Entity, Shell Company | false | ||
| Entity, Public Float | $ 147,000,000 | ||
| Entity, Common Stock Shares, Outstanding | 54,273,804 | ||
| Amendment Description | Alaska Communications Systems Group, Inc. and its consolidated subsidiaries (“we,” “our,” “us,” the “Company” and “Alaska Communications”) is filing this Amendment No. 1 on Form 10-K/A for the year ended December 31, 2020 (“Amendment”) to amend our Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission (the “SEC”) on March 16, 2021 (the “Original Form 10-K”). We are filing this Amendment to (i) present in Part I, Item 1A, a revised risk factor, as described in Item 503(c) of Regulation S-K, that is applicable to the Company [required if there are changes from the original 10-K]; and (ii) present the information required by Part III of Form 10-K that was previously omitted from the Original Form 10-K in reliance on General Instruction G(3) to Form 10-K. The Company is hereby amending the Original Form 10-K as follows: | ||
| Amendment Flag | true | ||
| Entity, Central Index Key | 0001089511 |
