Leasing activity in the third quarter for office space in Manhattan dipped below a 10-year rolling average for the first time since 2013, a crack in an otherwise robust commercial real estate market, Colliers International Group Inc said on Wednesday. NEW YORK: Leasing activity in the third quarter for office space in Manhattan dipped below a 10-year rolling average for the first time since 2013, a crack in an otherwise robust commercial real estate market, Colliers International Group Inc said on Wednesday.