Mack-Cali had signaled at the end of last year that it was training its sights on these trends when it announced a joint venture with Ironstate Development to add a highrise residential tower to its Harborside Financial Center in Jersey City. Last December, Hartz Mountain Industries, another company that had predominantly focused on office developments, broke ground on a joint venture with Roseland to build apartments in Weehawken.

After Mack-Cali's announcement that it will actually swallow Roseland whole, the architect of the deal—Bruce Schonbraun of FTI Consulting—described it as a "strategic, transformational diversification" for Mack-Cali, which is one of the largest owners of class A office space in the region.

Uranowitz says that virtually all of the "smart money" is flowing and shifting into multifamily development and trades right now for these reasons: New Jersey residents are flocking to a post-recession lifestyle of apartment living, due to affordability and the appeal of transit-oriented locations; that steady stream of demand positions multifamily property as a stable investment in a generally uncertain marketplace; and historic low interest rates are generating unprecedented building sales.

Mack-Cali and Roseland as separate firms have focused on developing class A portfolios, with both building signature properties on the Hudson riverfront—Mack-Cali's Harborside, for example, and Roseland's Port Imperial residential complex.

Uranowitz notes that investment activity is percolating at all levels of multifamily, however, including "B, C, even D—if there is such a thing as D."