equation goes out of margin

\[
 \left| \dfrac{(1-\beta e^{i\theta}) \sum_{k=2}^{\infty}(k-1)[1+\gamma(k-1)]
 \alpha_k\beta_k z^k}{B(1-\beta e^{i\theta}) \sum_{k=2}^{\infty}(k-1)[1+\gamma(k-1)] 
 \alpha_k \beta_k z^k -[(A-B)(1-\alpha)][z+\sum_{k=2}^{\infty}[1+\gamma(k-1)]
 \alpha_k \beta_k z^k]}\right|<1
\]