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.

Stocks with notable insider activity is something that I tweet about on a regular basis. These are also the exact type of stocks that I love to trade and alert in real-time.

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.

pdvWireless

One technology player that insiders are jumping into here is pdvWireless  (PDVW - Get Report) , which operates as a private wireless communications carrier, and provider of mobile workforce communication and location based solutions in the U.S. Insiders are buying this stock into large weakness, since shares have fallen sharply by 36.6% over the last three months.

pdvWireless has a market cap of $343 million and an enterprise value of $192 million. This stock trades at a premium valuation, with a price-to-sales of 96.82 and a price-to-book of 1.31. Its estimated growth rate for this year is 5.2%, and for next year it's pegged at 11.6%. This is a cash-rich company, since the total cash position on its balance sheet is $153.46 million and its total debt is $991,000.

A beneficial owner just bought 28,096 shares, or about $626,000 worth of stock at $21.57 to $23.44 per share. From a technical perspective, pdvWireless is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been uptrending over the last month or so, with shares moving higher off its low of $19.27 a share to its recent high of $24.83 a share. During that uptrend, shares of pdvWireless have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed this stock within range of triggering a near-term breakout trade.

If you're bullish on pdvWireless, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $21.88 a share and then once it breaks out above some near-term overhead resistance at $24.83 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 108,703 shares. If that breakout develops soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at its 50-day moving average of $26.89 a share or its 200-day moving average of $28.26 a share, or even $30 to $31.50 a share.

Colliers International Group

Another financial player that insiders are loading up on here is Colliers International Group  (CIGI - Get Report) , which provides commercial real estate services to real estate occupiers, owners and investors worldwide. Insiders are buying this stock into notable weakness, since shares have fallen by 11.6% over the last six months.

Colliers International Group has a market cap of $1.4 billion and an enterprise value of $1.6 billion. This stock trades at a fair valuation, with a trailing price-to-earnings of 142 and a forward price-to-earnings of 13.5. Its estimated growth rate for this year 6.6%, and for next year it's pegged at 10.7%. This is not a cash-rich company, since the total cash position on its balance sheet is $107.47 million and its total debt is $348.89 million.

A beneficial owner just bought 34,388 shares, or about $1.17 million worth of stock, at $34.17 per share.

From a technical perspective, Colliers International Group is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock recently formed a triple bottom chart pattern, after shares found some buying interest at $33.05, $33.03 and $32.93 a share. Following that bottom, shares of Colliers International Group have now started to uptrend and move back above its 20-day moving average of $35.34 a share. That move has now pushed this stock within range of triggering a near-term breakout trade.

If you're bullish on Colliers International Group then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $35.34 a share and then once it breaks out above some near-term overhead resistance levels at its 50-day moving average of $37.49 a share to $38.30 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 49,009 shares. If that breakout materializes soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at its 200-day moving average of $39.66 a share to $40.16, or even $43 a share.

Liberty Tax

One personal services player that insiders are jumping into here is Liberty Tax  (TAX) , which provides tax preparation services and solutions in the U.S. and Canada. Insiders are buying this stock into big weakness, since shares have dropped by 22% over the last six months.

Liberty Tax has a market cap of $320 million and an enterprise value of $208 million. This stock trades at a cheap valuation, with a trailing price-to-earnings of 10 and a forward price-to-earnings of 7.5. Its estimated growth rate for this year 2.8%, and for next year it's pegged at 27.6%. This is not a cash-rich company, since the total cash position on its balance sheet is $9.91 million and its total debt is $23.55 million.

A director just bought 20,200 shares, or about $264,000 worth of stock, at $13.06 to $13.25 per share.

From a technical perspective, Liberty Tax is currently trending above its 50-day moving average and well below its 200-day moving average, which is neutral trendwise. This stock has been uptrending very strong over the last three months, with shares moving higher off its low of $9.83 a share to its intraday high on Wednesday of $14.39 a share. During that uptrend, shares of Liberty Tax has been consistently making higher lows and higher highs, which is bullish technical price action.

If you're in the bull camp on Liberty Tax, then I would look for long-biased trades as long as this stock is trending above some near-term support t $13.50 a share or above its 20-day moving average of $12.83 a share and then once it breaks out above some near-term overhead resistance levels at $14.50 to $15 a share with volume that hits near or above its three-month average action of 82,336 shares. If that breakout kicks off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $16.50 to its 200-day moving average of $17.79 a share.

ITT Educational Services

One education and training services player that insiders are active in here is ITT Educational Services  (ESI - Get Report) , which provides postsecondary degree programs in the U.S. Insiders are buying this stock into large weakness, since shares have dropped sharply by 20.1% over the last six months.

ITT Educational Services has a market cap of $49 million and an enterprise value of $142 million. This stock trades at a fair valuation, with a trailing price-to-earnings of 2.9 and a forward price-to-earnings of 9.9. Its estimated growth rate for this year is -60.9, and for next year it's pegged at -51.2%. This is not a cash-rich company, since the total cash position on its balance sheet is $108.66 million and its total debt is $201.93 million.

A beneficial owner just bought 350,642 shares, or about $671,000 worth of stock, at $1.88 per share.

From a technical perspective, ITT Educational Services is currently trending below its 200-day moving average and above its 50-day moving average, which is neutral trendwise. This stock has been uptrending over the last month and change, with shares moving higher off its low of $1.57 a share to its intraday high on Wednesday of $2.15 a share. During that uptrend, shares of ITT Educational Services have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed this stock within range of triggering a near-term breakout trade.

If you're bullish in ITT Educational Services, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $1.91 a share and then once it breaks out above some near-term overhead resistance levels at $2.28 to around $2.30 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 419,703 shares. If that breakout fires off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $2.65 to its 200-day moving average of $2.84, or even $3 a share.

U.S. Geothermal

My final stock with some decent insider buying is renewable energy player U.S. Geothermal  (HTM) , which focuses on the development, production and sale of electricity from geothermal energy in the Western U.S. Insiders are buying this stock into major strength, since shares have soared by 43.4% over the last six months.

U.S. Geothermal a market cap of $95 million and an enterprise value of $180 million. This stock trades at a premium valuation, with a trailing price-to-earnings of 79 and a forward price-to-earnings of 29. This is not a cash-rich company, since the total cash position on its balance sheet is $7.43 million and its total debt is $92.47 million.

A director just bought 413,500 shares, or about $351,000 worth of stock, at 85 cents per share.

From a technical perspective, U.S. Geothermal is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending over the last six months, with shares moving higher off its low of around 50 cents per share to its recent high of 87 cents per share. During that uptrend, shares of U.S. Geothermal has been consistently making higher lows and higher highs, which is bullish technical price action.

If you're bullish on U.S. Geothermal, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of 82 cents per share or above its 50-day moving average of 80 cents per share and then once it breaks out above its 52-week high of 87 cents per share with volume that hits near or above its three-month average action of 361,069 shares. If that breakout hits soon, then this stock will set up to enter new 52-week-high territory, which is bullish technical price action. Some possible upside targets off that move are $1 to $1.20 a share.

Disclosure: This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.