I don't have a list to find the highest, but I suspect that [Spektr-R][1] (used for long baseline radio interferometry) is one of the highest altitudes that isn't associated with a Lagrange orbit.

The moon interacts with its orbit, so the apogee changes over time.  According to the [User Handbook][2] 

[![enter image description here][3]][3]

>  the apogee distance will vary from 286,938 to 371,233 km

It has a very high eccentricity, so I believe there are others with a greater semi-major axis.  I'm not sure which measure the question might want for "farthest out"


  [1]: https://en.wikipedia.org/wiki/Spektr-R
  [2]: http://www.asc.rssi.ru/radioastron/documents/rauh/en/rauh.pdf
  [3]: https://i.sstatic.net/uwWsQ.jpg