Removing PlaceholderFragment.
Adding code to launch a detail Fragment upon clicking any item in the adapter.
Moved all Fragment transaction back to the ListingActivity to manage the Fragments. Added a listener to be implemented by the ListingActivity when an adapter item is clicked, and then replace fragments.
Removing addToBackStack call on the ListingsFragment launch. Apparently no need to save to backStack to get the behavior I want.
Adding code to launch the DetailFragment with the ListingData from the clicked Position in the AdapterView. Using Parcelable to pass Listings around. Seems to work great.