DELAFIELD, Wis. (Stockpickr) -- Corporate insiders sell their own companies' stock for a number of reasons.

They might need the cash for a big personal purchase such as a new house or yacht, or they might need the cash to fund a charity. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price.

Other times they sell because they think their stock is overvalued and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge that a competitor is eating their lunch and stealing market share.

But insiders usually buy their own shares for one reason: They think the stock is a bargain and has tremendous upside.

The key word in that last statement is "think." Just because a corporate insider thinks his or her stock is going to trade higher, that doesn't mean it will play out that way. Insiders can have all the conviction in the world that their stock is a buy, but if the market doesn't agree with them, the stock could end up going nowhere. Also, I say "usually" because sometimes insiders are loaned money by the company to buy their own stock. Those loans are often sweetheart deals and shouldn't be viewed as organic insider buying.

At the end of the day, it's institutional money managers running big mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity but twice as important to make sure the trend of the stock coincides with the insider buying.

Recently, a number of companies' corporate insiders have bought large amounts of stock. These insiders are finding some value in the market, which warrants a closer look at these stocks.

Radius Health

One biopharmaceutical stock that insiders are active in here is Radius Health  (RDUS - Get Report), which focuses on developing novel therapeutics for patients with osteoporosis and other serious endocrine-mediated diseases in the U.S. Insiders are buying this stock into massive strength, since shares have exploded higher by 200% over the last six months.

Radius Health has a market cap of $1.5 billion and an enterprise value of $1.5 billion. This stock trades at a premium valuation, with a price-to-book of 60.8. Its estimated growth rate for next year is 29.2%. This is a cash-rich company, since the total cash position on its balance sheet is $68.51 million and its total debt is $24.32 million.

A beneficial owner just bought 75,000 shares, or about $3.53 million worth of stock, at $47.08 per share.

From a technical perspective, RDUS is currently trending above its 50-day moving average, which is bullish. This stock has been uptrending very strong for the last six months, with shares moving higher from its low of $13.16 to its recent high of $51.22 a share. During that uptrend, shares of RDUS have been consistently making higher lows and higher highs, which is bullish technical price action. Shares of RDUS are now starting to trend within range of triggering a major breakout trade above some key overhead resistance level.

If you're bullish on RDUS, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $44.01 or above more near-term support at $42.07 a share and then once it breaks out above its all-time high of $51.22 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average volume of 533,158 shares. If that breakout triggers soon, then RDUS will set up to enter new all-time-high territory, which is bullish technical price action. Some possible upside targets off that breakout are $55 to $60 a share, or even $65 a share.

Helix Energy Solutions Group

Another stock that insiders are jumping into here is Helix Energy Solutions Group  (HLX - Get Report), which provides specialty services to the offshore energy industry primarily in the Gulf of Mexico, North Sea, the Asia Pacific and West Africa regions. Insiders are buying this stock into major weakness, since shares have fallen by 38% over the last three months.

Helix Energy Solutions Group has a market cap of $1.4 billion and an enterprise value of $1.5 billion. This stock trades at a cheap valuation, with trailing price-to-earnings of 7.4 and a forward price-to-earnings of 10.6. Its estimated growth rate for this year is 59.3%, and for next year it's pegged at 79.2%. This is not a cash-rich company, since the total cash position on its balance sheet is $476.49 million and its total debt is $551.93 million.

The CEO just bought 71,500 shares, or above $1 million worth of stock, at $13.98 to $14 per share.

From a technical perspective, HLX is currently trending well below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending badly for the last three months, with shares moving lower from its high of $27.70 to its new 52-week low of $13.64 a share. During that downtrend, shares of HLX have been making mostly lower highs and lower lows, which is bearish technical price action. That said, shares of HLX have now entered oversold territory, since its current relative strength index reading is 26.29. Oversold can always get more oversold, but it's also an area where a stock can experience a powerful rebound higher from.

If you're in the bull camp on HLX, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $13.64 a share and then once it breaks out above some near-term overhead resistance levels at $14.53 to $15 a share and then above $16 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average action of 1.86 million shares. If that breakout begins soon, then HLX will set up to re-test or possibly take out its next major overhead resistance levels at $17 to its 50-day moving average of $18.15 a share, or even $19 a share.

Fox Factory

One recreational vehicles player that insiders are in love with here is Fox Factory  (FOXF - Get Report), which designs, engineers, manufactures and markets ride dynamics products worldwide. Insiders are buying this stock into modest strength, since shares have trended higher by 4.2% over the last three months.

Fox Factory has a market cap of $559 million and an enterprise value of $598 million. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 20.6 and a forward price-to-earnings of 13.4. Its estimated growth rate for this year is 6.8%, and for next year it's pegged at 19.1%. This is not a cash-rich company, since the total cash position on its balance sheet is $4.21 million and its total debt is $50 million.

A director just bought 100,000 shares, or about $1.48 million worth of stock, at $14.87 per share.

From a technical perspective, FOXF is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been uptrending a bit over the last few weeks, with shares moving higher from its low of $14.32 to its intraday high on Tuesday of $15.31 share. During that uptrend, shares of FOXF have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of FOXF within range of triggering a near-term breakout trade above some key overhead resistance levels.

If you're bullish on FOXF, then I would look for long-biased trades as long as this stock is trending above its recent low of $14.32 a share and then once it breaks out above both its 50-day at $15.61 a share and its 200-day at $15.73 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 85,818 shares. If that breakout develops soon, then FOXF will set up to re-test or possibly take out its next major overhead resistance levels at $16.29 to $16.55 a share, or even $17.08 a share. Any high-volume move above $17.08 a share will then give FOXF a chance to tag its next major overhead resistance levels at $18 to its 52-week high of $19.05 a share.

Albany Molecular Research

Another stock that insiders are making moves in here is Albany Molecular Research  (AMRI), which provides integrated drug discovery, development and manufacturing services primarily in the U.S., Europe and Asia. Insiders are buying this stock into decent strength, since shares have trended to the upside by 11.5% over the last three months.

Albany Molecular Research has a market cap of $557 million and an enterprise value of $666 million. This stock trades at a reasonable valuation, with a forward price-to-earnings of 18.7. Its estimated growth rate for this year is 30.2%, and for next year it's pegged at 17.1%. This is not a cash-rich company, since the total cash position on its balance sheet is $46.99 million and its total debt is $159.98 million.

The CEO just bought 20,000 shares, or about $354,000 worth of stock, at $17.70 per share.

From a technical perspective, AMRI is currently trending above its 50-day moving average and just below its 200-day moving average, which is neutral trendwise. This stock recently formed a major bottoming chart pattern, after shares found buying interest at $15.83, $15.76 and $15.91 a share. That bottom took place right around or just above its 50-day moving average. Shares of AMRI have now started to spike higher off those support levels and it's beginning to trend within range of triggering a major breakout trade above some key overhead resistance levels.

If you're bullish on AMRI, then I would look for long-biased trades as long as this stock is trending above those recent major bottom support levels and then once it breaks out above some near-term overhead resistance levels at $18.09 to its 200-day moving average of $18.61 a share and then above its gap-down-day high from last November at right around $19 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average action of 547,325 shares. If that breakout gets going soon, then AMRI will set up to re-fill its previous gap-down-day zone from last November that started near $23 a share.

Seattle Genetics

One final stock with some monster insider buying is Seattle Genetics  (SGEN - Get Report), a biotechnology company that develops and commercializes antibody-based therapies for the treatment of cancer. Insiders are buying this stock into decent strength, since shares have risen by 8.3% over the last three months.

Seattle Genetics has a market cap of $4.6 billion and an enterprise value of $4 billion. This stock trades at a premium valuation, with a price-to-sales of 15.1 and a price-to-book of 20.5. Its estimated growth rate for this year is -14.5%, and for next year it's pegged at 53.5%. This is a cash-rich company, since the total cash position on its balance sheet is $313.41 million and its total debt is zero.

A director just bought 448,841 shares, or about $15.63 million worth of stock, at $34.76 to $34.82 per share.

From a technical perspective, SGEN is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending over the last month and change, with shares moving higher from its intraday high on Tuesday of $37.89 a share. During that uptrend, shares of SGEN have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of SGEN within range of triggering a near-term breakout trade.

If you're bullish on SGEN, then I would look for long-biased trades as long as this stock is trending above some key near-term support at $34.21 a share or above its 50-day moving average of $32.95 a share and then once it breaks out above Tuesday's intraday high of $37.89 to more resistance around $38 a share with high volume. Look for a sustained move or close above the levels with volume that hits near or above its three-month average volume of 1.31 million shares. If that breakout hits soon, then SGEN will set up to re-test or possibly take out its next major overhead resistance levels at $40.35 to $42 a share, or even $45 to around $48 a share.

This article is commentary by an independent contributor. At the time of publication, the author held TK positions in the stocks mentioned.