I wonder if the following problem is NP-hard. Is it?

Given a bipartite graph $G = (U, V, E)$ with weights $w : E \to \mathbb{R}_+$, find a partition of $U$ into $U_1, U_2$ and nonempty disjoint subsets $V_1, V_2 \subseteq V$ such that

$$w(U_1, V_1)+w(U_2, V_2) - w(U_1, V_2) - w(U_2, V_1)$$

is maximal, where

$$w(U_i, V_j):= \sum\limits_{e \in E(U_i,V_j)}w(e)$$