Part-year resident of two states?

We moved to our second home in AZ in late Jan 2015 but our permanent residence is in DC. We traveled back and forth between residences during the year. Our state of residence on 31 December 2015 was DC; however, the next Turbo Tax question is "Previous state of residence." AZ is not our previous state of residence. I then need to indicate the date I became a resident of DC when AZ is the new state. How do I handle this situation?