Yes, Sitecore can be installed in offline mode, or from machines without internet access.
The latest versions of Sitecore Instance Manager, since the version 126.96.36.199 release, supports running in offline mode. Earlier versions were not able to run in offline mode but you should upgrade to the latest version (188.8.131.52) if you have not already done so.
You can also install Sitecore without the use of SIM. In all versions prior to 9 you are able to download an exe application installer, which will run offline, create the necessary IIS site + bindings, add the hosts file entry and attach the SQL databases:
Alternatively, you can install the application manually by downloading the zip archive of the site root folder, extracting the files, creating an IIS site + binding manually, attaching the SQL Server databases and then editing the Sitecore config files for your local set up. The installation process for both of these methods is heavily documented in the Sitecore Installation Guide for each version.