From what I know about idealism, I can say with full confidence that to equate Buddhism with idealism is very wrong as their views differ quite substantially. Actually, no one really thinks of Buddhism as idealism, only that religion in general is viewed as such, which in the case of Western religion is not incorrect.

In summary, Buddhism is not idealism because it does not deem the ultimate nature of reality is based on mind or mental phenomena; neither is it materialism as it does not consider the ultimate nature of reality is based on physical phenomena.

~Depicted THE RIGHT VIEW - Buddhism—the Definition