Los Angeles is losing the resident company of fiction, nonfiction and screenwriters Joan Didion and John Gregory Dunne, Dunne said Thursday. The pair, who have lived in Los Angeles for 24 years, are moving to New York. "We just didn't care for the idea of being legitimately 'bi-coastal'," Dunne said from New York. "The time was right--neither Joan nor I had anything we were right in the middle of, and --to quote Lenin--there is nothing like the power of an idea whose time had come. We loved L.A. a lot, but we were due for a change." The couple plan to continue their screen work, writing original scripts as well as films based on their own works: "Salvador" and "The White Album" for Didion; "The Red, White and Blue" for Dunne.