Any rehab lasting longer than 3 months is considered long term rehab.
Statistically, this is the therapeutic program most likely to bring about a life of sobriety. However, it is rarely the choice for first time treatment. Long term rehab is generally chosen in response to years of abuse and repeated relapses.
Quite simply it provides time. This time is used for the severe addict to heal, make changes and learn to enjoy life while maintaining sobriety.
Find a rehab that specializes in long term treatment.