• Insider buying can be an encouraging signal for potential investors, especially when markets are near all-time highs.
• Once again, some insiders took advantage of recent public share offerings to add or bolster stakes.
• Again, biotechnology companies are well represented on this list.

Conventional wisdom says that insiders and 10% owners really only buy shares of a company for one reason -- they believe the stock price will rise and they want to profit from it. So insider buying can be an encouraging signal for potential investors, particularly when there is uncertainty in the markets or the markets are near all-time highs.

Note that, with the earnings reporting season still underway, many insiders are prohibited from buying or selling shares. Here are some of the most noteworthy insider purchases that were reported in the past week.

The combined 3.52 million or so Impel Neuropharma Inc IMPL shares that five beneficial owners purchased had an initial public offering price of $15.00 per share. These transactions cost them more than $52.87 million. The stock has traded as high as $15.89 a share since the offering but ended the week at $15.20.

Rain Therapeutics Inc RAIN saw two beneficial owners and a former 10% owner buy into the IPO. The more than 2.02 million shares of this oncology company acquired altogether, at $17.00 apiece, added up to over $34.42 million. The stock ended the week trading at $16.37 per share.

A Knowbe4 Inc KNBE a beneficial owner indirectly scooped up almost 1.88 million shares early last week. At the IPO price of $16.00 a share, that totaled about $30.00 million for the security awareness platform provider. The stock has traded as high as $26.98 a share but ended the week at $22.98.

A 10% owner of Beacon Roofing Supply, Inc. BECN added to its stake last week. The more than 563,600 shares indirectly bought at around $53.23 apiece totaled nearly $30.00 million and lifted the stake to about 14.32 million shares. The stock hit a 52-week high of $57.67 on Friday.

New Jersey-based real estate investment trust (REIT) Mack Cali Realty Corp CLI had a director return and indirectly pick up 200,000 more shares at around $16.46 a share. That cost that director more than $3.39 million. Note that the same director also purchased almost 240,000 shares previously.

Apollo Medical Holdings Inc AMEH saw a beneficial owner pay $24.50 apiece for 100,000 shares. The total for this transaction was $2.45 million, and it lifted the stake to over 10.75 million shares. Note that the company's chief medical officer also sold 100,000 shares at about the same time.

Swimming pool maker Latham Group Inc SWIM  just had its IPO too. CEO Michael Rajeski and several other insiders picked up 127,500 shares altogether for $19.00 apiece. These purchases added up to more than $2.42 million. The stock has traded as high as $28.98 a share but ended the week at $26.00.

A 10% owner added 47,700 more shares of AnaptysBio Inc ANAB last week. They were acquired indirectly for between $23.53 and $23.82 apiece, which totaled more than $1.13 million and lifted the stake in this San Diego-based biotech to almost 7.30 million shares.

Chipotle Mexican Grill, Inc. CMG saw a director buy 673 shares at $1,485 apiece. That cost him in the neighborhood of $999,400. Note though that an officer parted with almost 2,800 shares more recently. The stock was last seen trading at $1,492.03 per share, and Jim Cramer recently said it could go "much higher."

Note that some smaller amount of insider buying at Arcus Biosciences Inc RCUS, Associated Banc Corp ASB, Capstar Financial Holdings Inc CST, Heartland Express, Inc. HTLD, Tellurian Inc TELL, Texas Capital Bancshares Inc TCBI and Texas Pacific Land Corp TPL  was reported in the past week as well.