One way individual investors can find lucrative ideas is by following smart investment managers and note what stocks they own in their portfolios. Take Bill Ackman, the billionaire hedge fund manager of Pershing Square Capital Management. He runs a very concentrated book that focuses on what he believes are high-quality businesses with a long-term mindset. Chipotle Mexican Grill (NYSE: CMG) is one of Ackman's top holdings, representing 18.2% of the portfolio as of Dec. 31. Ackman's firm has owned the restaurant stock since the third quarter of 2016 at an initial cost basis of about $411 per share.