Long Distance
A far distance detachment is a distance that is far. It is long distance. Also remember that 距離 is a "distance" so a far distance is a long distance.
えんきょり
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
日本では、遠距離通学や遠距離通勤はよくあることです。
In Japan, having a long distance commute to school or work is pretty common.