Take a look at some of Thursday's midday movers:
Red Robin Gourmet Burgers plummeted after the fast-casual dining chain reported a surprise drop in net income for the second quarter.
NewLink Genetics moved higher after the Iowa drug developer said it is ready to start human testing for a possible Ebola vaccine.
SeaWorld continued to fall, a day after reporting weaker-than-expected earnings due to falling attendance. Today, four firms downgraded the stock.
Berkshire Hathaway Class A stock moved higher, surpassing the $200,000 a share level for the first time ever.
Perrigo was the best performer on the S&P 500 after the maker of over-the-counter store brand drugs reported better-than-expected fourth-quarter results.
Vipshop plummeted despite the online discount retailer reporting stronger-than-expected second-quarter results.
Merck advanced after the drug company won federal approval for a new type of sleeping pill designed to help people with insomnia stay asleep.
Weyerhaeuser gained ground after the timberlands holder raised its quarterly dividend 32 percent and unveiled a $700 million share buyback program.
Advance Auto Parts moved higher after posting better-than-expected second-quarter earnings.
Re/Max Holdings climbed after posting better-than-expected second-quarter revenue.
Intermune fell after Goldman Sachs downgraded the biotech firm to "neutral" from "buy" due to valuation.
Ally Financial gained ground after the Treasury Department said it plans to publicly sell shares of the auto lender.
Plug Power rose after the firm's quarterly revenue more than doubled, as fuel cell demand soars.
Aruba Networks rose after Stifel Nicolaus upgraded the stock "buy," saying the wireless network equipment maker had solid momentum last quarter while pricing pressures eased.