In the basic resources.hbs file, the button for all has "selected" as a part of its class. If you moved that to the document button, that might do the trick.
| <button class="base resources-show-all selected" data-filter="all" aria-label="{{model._filterAria.allAria}}" tabindex="0"> |
| <button class="base resources-show-document selected" data-filter="document" aria-label="{{model._filterAria.documentAria}}" tabindex="0"> |