The deal is complex. One part calls for the buyer to pay Casden Properties founder Alan Casden and his partner, an affiliate of Blackacre Capital Management, about $166 million in cash, $213 million in stock and other securities, and to assume about $684 million of the partnership's mortgage debt.

Apartment Investment & Management Co., commonly called Aimco, will also take control of 1,381 apartment units that Casden is building near the Fairfax District's sprawling Park LaBrea housing complex in exchange for $419 million in cash and the assumption of debt.

Casden Properties already owns about 17,400 apartment units, primarily in Southern California. It is in various stages of developing another 6,700 units.