Dollar General said Friday that it's extended its hostile bid for Matthews, N.C.-based Family Dollar until Dec. 31. The $80 per share, all-cash bid had been set to expire at the end of the day Friday. Family Dollar has rebuffed Dollar General's advances, with the company's board of directors turning down Dollar General's bids so far. Instead, Family Dollar's board wants to complete a previously announced acquisition by rival discount retailer Dollar Tree, which the companies agreed to in July. Family Dollar shareholders are set to vote on the Dollar Tree deal Dec. 11 in Charlotte.