For Mid-America Apartment Communities, the Sunbelt is where it's at. Operating as MAA, the firm is a self-administered, self-managed real estate investment trust (REIT) that focuses solely on buying multifamily residences. MAA owns or has interests in approximately 79,500 apartment units in 15 states, primarily located in the West, Southeast and south-central US. Its largest markets are California, Florida, Tennessee, and Texas. MAA, which has an average property occupancy rate of 95%, targets large and midsized markets. MAA bought rival Colonial Properties in 2013 in an $8.6 billion deal. It is now buying Post Properties for $3.9 billion to become the nation's largest public apartment owner by unit number.