The stock market has performed extremely well recently, with the S&P 500 index higher by 17% over the past six months. Many stocks have done far better, doubling or more in that short amount of time. A stock that has been an excellent performer can still be worth buying, despite the higher price. Here are three in particular that still look like exciting long-term investments despite rising by 100% or more over the last six months. Image source: Getty Images. These three stocks have doubled (or more) in just six months Company (Symbol) Industry 6-Month Performance Pinterest (NYSE: PINS) Social Media 116% Boston Omaha (NASDAQ: BOMN) Conglomerate 145% Lemonade (NYSE: LMND) Insurance 119% S&P 500 (for reference) N/a 17% Data source: YCharts. Six-month returns as of 2/3/2021. All three have performed well for good reasons. Pinterest gained over 100 million users in the past year, Lemonade's revenue has more than doubled, and some of Boston Omaha's key investments have performed very well. There could still be plenty of room to climb Although these stocks more than doubled in just six months, there could be plenty of room to grow in the years ahead. Pinterest still has a massive opportunity to monetize its user base, especially internationally. The average international Pinterest user generates roughly 5% of the revenue of its domestic users. Since over three-fourths of Pinterest's user base is international, even a small narrowing of the gap could be a game-changer. Plus, since Pinterest's main use case is a place people go for ideas, there are some natural e-commerce opportunities that the company has just started to explore. Boston Omaha Corporation is often compared to an early Berkshire Hathaway, and it's easy to see why. The company's business model involves acquiring subsidiaries and other investments, which can then generate cash flow to acquire even more. In addition to growth opportunities in its main businesses (billboards, insurance, and rural broadband), Boston Omaha recently launched a SPAC called Yellowstone Acquisition. One of its larger investments, Dream Finders Homes, also just completed a very successful IPO. With a market cap roughly 0.2% of Berkshire's size, it could still have quite a long way to let its time-tested business model play out. Last but certainly not least, insurance technology company Lemonade has taken its core markets of homeowners, renters, and pet insurance by storm, with gross earned premiums more than doubling in the most recent quarter. To put Lemonade's impressive growth into perspective, consider that the company just hit 1 million customers in a little over four years in business, an accomplishment that took State Farm and GEICO 22 and 28 years to achieve, respectively. However, Lemonade is just starting to dip its toes into the $800 billion term life insurance market, and that's the most exciting opportunity right now. If Lemonade can replicate its success and capture a large share of the life insurance market, the recent performance could be just the beginning. These companies are long-term winners; invest accordingly Investors must remember that a top-performing stock can continue to deliver strong results. It's a common mistake to say, "Well, this stock has done well, let's look for something cheaper." All three of these companies have impressive growth opportunities going forward. These stocks have gone up for solid reasons, and could certainly give the market reasons why they're worth even more. Find out why Pinterest is one of the 10 best stocks to buy now Motley Fool co-founders Tom and David Gardner have spent more than a decade beating the market. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* Tom and David just revealed their ten top stock picks for investors to buy right now. Pinterest is on the list -- but there are nine others you may be overlooking. Click here to get access to the full list! *Stock Advisor returns as of November 20, 2020 Matthew Frankel, CFP owns shares of Boston Omaha, Lemonade, Pinterest, Yellowstone Acquisition Company, and Berkshire Hathaway (B Shares). The Motley Fool owns shares of and recommends Boston Omaha, Lemonade, Inc., and Pinterest. The Motley Fool owns shares of and recommends Berkshire Hathaway (B shares) and recommends the following options: short March 2021 $225 calls on Berkshire Hathaway (B shares), short January 2023 $200 puts on Berkshire Hathaway (B shares), and long January 2023 $200 calls on Berkshire Hathaway (B shares). The Motley Fool has a disclosure policy.Source