Singapore developers struggling to sell apartments in their home market are buying property overseas, turning the island-state into the largest foreign investor from the region this year. Companies including City Developments Ltd. and Keppel Land Ltd. pumped $2.32 billion into overseas markets in the nine months through September, a threefold increase from the same period last year and the most in at least eight years, according to data from Real Capital Analytics Inc., a research firm that specializes in investments in commercial property.