Shares of Lockheed Martin Corp. LMT, -1.33% declined in the extended session Thursday while shares of Boeing Co. BA, -3.58% advanced following a tweet by President-elect Donald Trump about cost overruns for Lockheed's F-35 fighter. Lockheed shares fell 1.9% to $248 after hours, while Boeing shares rose 0.7% to $158.58. Late Thursday, Trump posted on his Twitter account that he had asked Boeing to price out a comparable F-18 Super Hornet fighter because of rising costs in the F-35 program.