Went out too little for them. The Hebrew is, went out from them; i.e; either went out beyond their own borders, or went out too small a distance to be sufficient for them. The first is the explanation of Masius ("extra se migrasse"), the second of Jarchi.
Houbigant suggests for וַיֵּצֵא "and it went out" וַיָּאָץ "and it was narrow." But the LXX, has the same reading as ourselves, and the explanation given above is quite consistent with the fact. The border of Dan did "go out" far beyond the borders originally assigned to the tribe, in fact to the extreme northern limit of Palestine.
The account of the taking of Laish, or Leshem, is given more fully in 18:1-31. The inheritance assigned to Dan was extremely small, but it was also extremely fertile.