Setting for Full-Width Page Default?

I cannot find anywhere to set the default page template for full-width. I've got a full-width template, and have manually selected that for my pages, but the generated pages (i.e. Archives, Blog Posts, etc) generate with a sidebar. I simply don't want a sidebar on ANY of my pages.

I've tried to edit my CSS to display: none; for the sidebar, which works- but unfortunately the rest of the content doesn't take up its vacant space. I've tried to edit the CSS to expand the #content #post-content to 95%, but there appears to be !important settings that are overriding and I'm lost trying to find out how to get around that. This obviously isn't the best way to go about it.

This in turn is also affecting my BuddyPress pages (i.e. Members), which are also rendering with a sidebar.

Please help.
Thank You.