In Example 1.4 of his book *Invariants of Homology 3-Spheres*, Saveliev noted that twist knots $K_n$ of type $(2n+2)_1$ are all hyperbolic. Here, $K_1$ is the figure-eight knot $4_1$ and $K_2$ is the stevedore knot $6_1$, see the following figure

Actually, this seems a well-known fact to experts but I couldn't find an explicit reference. Is there an easy way to see this?