Always calculate dimensions with editor on DOM

Closes #206

src/app/editor.coffee

@@ -804,6 +804,10 @@ class Editor extends View
     @overlayer.append(view)
 
   calculateDimensions: ->
+    if not @isOnDom()
+      detachedEditorParent = _.last(@parents()) ? this
+      $(document.body).append(detachedEditorParent)
+
     fragment = $('<pre class="line" style="position: absolute; visibility: hidden;"><span>x</span></div>')
     @renderedLines.append(fragment)
 
@@ -815,6 +819,8 @@ class Editor extends View
     @height(@lineHeight) if @mini
     fragment.remove()
 
+    $(detachedEditorParent).detach()
+
   updateLayerDimensions: ->
     @gutter.calculateWidth()