Cyclotomic Polynomials

Appropriate Level:  Abstract Algebra

The Question:  Recall that the cyclotomic polynomials $\Phi _n (x)$ are defined for $n \geq 1$ so that $\prod_{d|n} \Phi_d (x) = x^n -1$.  Is it true that every coefficient of every cyclotomic polynomial is either 0, 1, or -1?