Google docs team has added new type of version history which is now available for all the google docs document. Now you can see a more refined revision history on google docs document which will list all the users who has changed the document over a span of time.
In order to view revision history for a document, go to File >> View Revision History as shown in the image below.
However if you want to see more detailed version which includes what changes has been made by different users and when did they make those changes, you can click the button which says show more detailed revisions.
You can easily toggle to show the changes by checking or unchecking the option which says Show changes as shown in the image below.