How to get all values from a multiple select field in laravel controller

Basically, in my blade.php file or html file, I have a multiple select field. What I'm trying to do is get all selected field's ID and return it to my controller. How would I go about to do this?

Multiple Select in blade.php;

<div class="form-group">
   <label class="col-xs-12" for="users">Select User</label>
   <div class="col-sm-9">
     <select class="form-control" id="users" name="users" size="10" multiple="">
       @foreach($admin as $a)
       <option value="{{$r->id}}">{{$a->fullname}}</option>
       @endforeach
     </select>
   </div>
</div>

Controller that sends data;

public function assignRole() {

   $role = Role::all();
   $admin = Admin::all();

   return View::make("assignRole", compact('role', 'admin'));

} 

Controller that retrieves data;

public function assignNewRole(Request $request) {
   $data = $request->all();

   dd($data);

   return redirect()->route('role')->with('success', 'Successfully assigned role.');
}

I'm trying to see what I get in my "dd", but what i get now is;

array:3 [▼
  "_token" => "ongoBbjBaOXJrPleNSdYPsr8aJlb6CLUxHHkHKoP"
  "role" => "1"
  "users" => "2"
]

What i would want is maybe, "users" => "1", "3", "17". (a list of all the selected user id's).