The defense company's stock has had a strong run recently due to derisking the F-35 program and some improved margin performance.Lockheed Martin (LMT 1.90%) stock is up 13.7% this year, and most of the gain comes after the company's recent second-quarter earnings report. Does the good news from the second quarter signal a buying opportunity, or is now the time to take advantage of the increase in the share price? Here's a look at what happened and how to think about the stock.Lockheed Martin provides some p ...