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.

Syntel

One technology player that insiders are active in here is Syntel  (SYNT) , which provides digital transformation, information technology, and knowledge process outsourcing services worldwide. Insiders are buying this stock into large weakness, since shares have fallen by 57.6% over the last six months.

Syntel has a market cap of $1.6 billion and an enterprise value of $2 billion. This stock trades at a reasonable valuation, with a price-to-sales of 1.66. This is not a cash-rich company, since the total cash position on its balance sheet is $88.39 million and its total debt is $479.32 million.

A director just bought 20,000 shares, or about $389,000 worth of stock, at $19.50 per share.

From a technical perspective, Syntel is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been consolidating and trending sideways over the last few weeks, with shares moving between $18 on the downside and $20.55 on the upside. Any high-volume move above the upper-end of its recent sideways trending chart pattern could trigger a big breakout trade for shares of Syntel.

If you're bullish on Syntel then I would look for long-biased trades as long as this stock is trending above some key near-term support levels at $19.22 or above its new 52-week low of $18 a share and then once it breaks out above some near-term overhead resistance levels at $20 to $20.55 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 volume of 880,081 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 $22 to its 50-day moving average of $22.78 a share, or even $23 to $24 a share.

Post Holdings

Another consumer goods player that insiders are jumping into here is Post Holdings  (POST) which operates as a consumer packaged goods holding company in the U.S. and internationally. Insiders are buying this stock into modest weakness, since shares have fallen by 8.8% over the last three months.

Post Holdings has a market cap of $5 billion and an enterprise value of $8.7 billion. This stock trades at a fair valuation, with a forward price-to-earnings of 25.8. Its estimated growth rate for this year is 1.5%, and for next year it's pegged at 14.1%. This is not a cash-rich company, since the total cash position on its balance sheet is $1.14 billion and its total debt is $4.88 billion.

A director just bought 120,000 shares, or about $9.05 million worth of stock, at $74.45 per share.

From a technical perspective, Post Holdings is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending over the last few weeks, with shares moving higher off its low of $68.76 a share to its recent high of $78.33 a share. During that uptrend, shares of Post Holdings have been making mostly higher lows and higher highs, which is bullish technical price action.

If you're bullish on Post Holdings then I would look for long-biased trades as long as this stock is trending above some near-term support at $76 a share or above its 20-day moving average of $74.21 a share and then once it breaks out above some near-term overhead resistance levels at $79 to $80 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 905,492 shares. If that breakout takes hold soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $82 to $84, or even $87 to its 52-week high of $89 a share.

Starz

One entertainment player that insiders are active in here is Starz  (STRZA) , which operates as a media and entertainment company worldwide. Insiders are buying this stock into large strength, since shares have risen by 26.7% over the last six months.

Starz has a market cap of $3.3 billion and an enterprise value of $4.2 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 18.9. This is not a cash-rich company, since the total cash position on its balance sheet is $14 million and its total debt is $995.60 million.

A beneficial owner just bought 386,587 shares, or about $13.12 million worth of stock, at $33.94 per share.

From a technical perspective, Starz is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending over the last five months, with shares moving higher off its low of $25.05 a share to its recent high of $34.31 a share. During that uptrend, shares of Starz have been making mostly higher lows and higher highs, which is bullish technical price action. That uptrend has now pushed this stock within range of triggering a big breakout trade above some key overhead resistance levels.

If you're in the bull camp on Starz, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $32.10 a share or above more near-term support at $30.30 a share and then once it breaks out above some key overhead resistance levels at $34.31 to its 52-week high of $35.84 a share with volume that hits near or above its three-month average action of 1.40 million shares. If that breakout develops 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 breakout are $39 to $40, or even $42 to 43 a share.

Proteostasis Therapeutics

One biopharmaceutical player that insiders are in love with here is Proteostasis Therapeutics  (PTI) , which develops therapeutics to treat protein conformational diseases. Insiders are buying this stock into large weakness, since shares have dropped by 33.6% over the last six months.

Proteostasis Therapeutics has a market cap of $266 million and an enterprise value of $170 million. This stock trades at a premium valuation, with a price-to-sales of 48.7 and a price-to-book of 3.01. Its estimated growth rate for this year is -32.6%, and for next year it's pegged at -10.3%. This is a cash-rich company, since the total cash position on its balance sheet is $100.24 million and its total debt is zero.

A beneficial owner just bought 361,863 shares, or about $4.12 million worth of stock, at $10.67 per share.

From a technical perspective, Proteostasis Therapeutics is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the last few weeks, with shares moving lower off its high of $12.24 a share to its recent low of $10 a share. During that slight downtrend, shares of Proteostasis Therapeutics have been making mostly lower highs and lower lows, which is bearish technical price action.

If you're bullish on Proteostasis Therapeutics, then I would look for long-biased trades as long as this stock is trending above some near-term support levels at $10 or at $9 a share and then once it breaks out above some near-term overhead resistance levels at $11.50 to $12 a share and then above $12.24 to its 50-day moving average of $12.29 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 271,234 shares. If that breakout triggers soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $14.04 to $15 a share.

Paramount Group

My final stock with some large insider buying is financial player Paramount Group  (PGRE) , which is a real estate firm that invests in Class A office properties located in select central business district submarkets of New York City, Washington, D.C. and San Francisco. Insiders are buying this stock into modest weakness, since shares have dropped by 3.9% over the last six months.

Paramount Group a market cap of $4.1 billion and an enterprise value of $6.5 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 825 and a forward price-to-earnings of 17.6. Its estimated growth rate for this year is 4.9%, and for next year it's pegged at 4.7%. This is not a cash-rich company, since the total cash position on its balance sheet is $83.28 million and its total debt is $3.18 billion. This stock currently sports a dividend yield of 2.4%.

A director just bought 100,000 shares, or about $1.57 million worth of stock, at $15.74 per share.

From a technical perspective, Paramount Group is currently below both its 50-day and 200-day moving averages, which is bearish. This stock has been consolidating and trending sideways over the last few weeks, with shares moving between $15 on the downside and $16.32 on the upside. Any high-volume move above the upper-end of its recent sideways trending chart pattern could trigger a big breakout trade for shares of Paramount Group.

If you're bullish on Paramount Group, then I would look for long-biased trades as long as this stock is trending above some near-term support at $14 a share or above its recent low of $14.58 a share and then once it breaks out above its 200-day moving average of $16.20 a share to $16.32 a share with volume that hits near or above its three-month average action of 808,072 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 $17.30 to $18.20, or even its 52-week high of $18.56 a share.

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