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.

Cardiovascular Systems

One medical technology player that insiders are active in here is Cardiovascular Systems  (CSII - Get Report) , which develops, manufactures and markets devices to treat vascular diseases in the U.S. Insiders are buying this stock into massive weakness, since shares have plunged by 62.5% over the last six months.

Cardiovascular Systems has a market cap of $285 million and an enterprise value of $219 million. This stock trades at a reasonable valuation, with a price-to-sales of 1.54 and a price-to-book of 2.26. Its estimated growth rate for this year is -63.3%, and for next year it's pegged at 19.7%. This is a cash-rich company, since the total cash position on its balance sheet is $65.33 million and its total debt is zero.

A beneficial owner just bought 250,000 shares, or about $1.88 million worth of stock, at $7.55 per share.

From a technical perspective, Cardiovascular Systems 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 off its new 52-week low of $7.50 a share to its recent high of $8.99 a share. During that uptrend, shares of Cardiovascular Systems 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 major breakout trade.

If you're bullish on Cardiovascular Systems, then I would look for long-biased trades as long as this stock is trending above some near-term support at around $8 a share and then once it breaks out above some key near-term overhead resistance levels at $8.99 to $9.34 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 558,292 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 level at $9.95 a share. Any high-volume move above $9.95 will then give this stock a chance to re-fill some of its previous gap-down-day zone from January that started near $13 a share.

Incyte

Another biotechnology player that insiders are loading up on here is Incyte  (INCY - Get Report) , which focuses on the discovery, development, and commercialization of proprietary therapeutics in oncology. Insiders are buying this stock into big weakness, since shares have fallen sharply by 34.8% over the last six months.

Incyte has a market cap of $14 billion and an enterprise value of $13.9 billion. This stock trades at a reasonable valuation, with a forward price-to-earnings of 59. Its estimated growth rate for this year is 766.70%, and for next year it's pegged at 388.50%. This is a barely cash-rich company, since the total cash position on its balance sheet is $707.78 million and its total debt is $619.89 million.

A director just bought 64,290 shares, or about $4.55 million worth of stock, at $69.70 to $74 per share.

From a technical perspective, Incyte 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 $68.56 on the downside and $77.29 on the upside. This stock has now started to bounce higher right off its 20-day moving average of $72.17 a share and it's beginning to trend within range of triggering a big breakout trade above the upper-end of its recent sideways trending chart pattern.

If you're in the bull camp on Incyte, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $72.17 or above more near-term support at $69.50 a share and then once it breaks out above some key overhead resistance levels at $76.78 to $77.29 a share with volume that hits near or above its three-month average action of 2.38 million 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 $83.25 to $84.20, or even $90 a share.

Nexvet Biopharma

One stock that insiders are jumping into here is Nexvet Biopharma  (NVET) , which focuses on developing and commercializing novel, species-specific biologics based on human biologics for companion animals. Insiders are buying this stock into notable weakness, since shares have dropped by 25.1% over the last six months.

Nexvet Biopharma has a market cap of $38 million and an enterprise value of -$4.2 million. This stock trades at a fair valuation, with a price-to-book of 0.88. Its estimated growth rate for this year is 26.9%, and for next year it's pegged at -14.5%. This is a cash-rich company, since the total cash position on its balance sheet is $43.08 million and its total debt is zero.

A beneficial owner just bought 435,000 shares, or about $1.38 million worth of stock, at $3.18 to $3.36 per share.

From a technical perspective, Nexvet Biopharma is currently trending above its 50-day moving average and well below its 200-day moving average, which is neutral trendwise. This stock has recently carved out a double bottom chart pattern, after shares found some buying interest at $2.85 to $2.90 a share. Following that potential bottom, this stock has now started to trend higher and move back above its 20-day moving average of $3.15 a share. That move has now pushed this stock within range of triggering a big breakout trade above some near-term overhead resistance levels.

If you're bullish on Nexvet Biopharma, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $3.15 a share or above those recent double bottom support levels and then once it breaks out above some key near-term overhead resistance levels at $3.50 to $3.60 a share and then above $3.71 a share volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 50,007 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 $4 to $4.14, or even its 200-day moving average of $4.24 to $4.50 a share.

Archrock

One energy player that insiders are in love with here is Archrock  (AROC - Get Report) , which provides natural gas contract compression services to customers in the oil and natural gas industry in the U.S. Insiders are buying this stock into huge weakness, since shares have plunged lower by 78.9% over the last six months.

Archrock has a market cap of $315 million and an enterprise value of $2.3 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 7.2 and a forward price-to-earnings of 21.6. Its estimated growth rate for this year is 6%, and for next year it's pegged at 13.2%. This is not a cash-rich company, since the total cash position on its balance sheet is $32.52 million and its total debt is $2.09 billion. This stock currently sports a dividend yield of 18.8%.

A beneficial owner just bought 663,433 shares, or about $2.25 million worth of stock, at $3.58 to $3.94 per share.

From a technical perspective, Archrock is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the last four months, with shares moving sharply lower off its high of $14.02 to its new 52-week low of $3.40 a share. During that downtrend, shares of Archrock have been consistently making lower highs and lower lows, which is bearish technical price action. That said, this stock has now started to rip higher off that $3.40 low and it's quickly moving within range of triggering a near-term breakout trade.

If you're bullish on Archrock, then I would look for long-biased trades as long as this stock is trending above its new 52-week low at $3.40 a share and then once it breaks out above some near-term overhead resistance levels $4.60 to $5 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 897,648 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 $5.55 to $5.87, or even $$6 to $6.50 a share.

CNA Financial

One final stock with some large insider buying is financial player CNA Financial  (CNA - Get Report) , which provides commercial property and casualty insurance products primarily in the U.S. Insiders are buying this stock into notable weakness, since shares have dropped by 14.8% over the last six months.

CNA Financial has a market cap of $7.9 billion and an enterprise value of $8.5 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 16.7 and a forward price-to-earnings of 8.9. Its estimated growth rate for this year is 60%, and for next year it's pegged at 8.6%. This is not a cash-rich company, since the total cash position on its balance sheet is $2.05 billion and its total debt is $2.56 billion. This stock currently sports a dividend yield of 3.4%.

A beneficial owner just bought 49.900 shares, or about $1.44 million worth of stock at $29.89 per share. That same beneficial owner also just bought 111,900 shares, or about $3.19 million worth of stock at $28.48 to $28.73 per share. From a technical perspective, CNA Financial is currently trending below both its 50-day and 20-day moving averages, which is bearish. This stock has been uptrending a bit over the last few weeks, with shares moving higher off its low of $26.97 to its recent high of $29.79 a share. During that uptrend, shares of CNA Financial 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 CNA Financial, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $28.94 a share or above more key support at $28 a share and then once it breaks out above some near-term overhead resistance levels at $29.79 to its 50-day moving average of $30.41 a share and then above more resistance at $31 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 175,346 shares. If that breakout hits soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $32.50 to its 200-day moving average of $33.35, or even $34.50 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.