In a victory for common sense, the trading behavior of company executives, directors, and large shareholders in the stocks of firms they're registered "insiders" at have been proven profitable to monitor by both academic studies and (more importantly) the experience of your fellow professional investors.

Below are lists of the top 10 mainly open-market insider purchases and sales filed at the Securities and Exchange Commission Thursday, February 21, 2013 as ranked by dollar value.

Please note, however, that these are factual lists, not buy and sell recommendations. Dollar value is only one metric to assess the importance of an insider transaction, and, frankly, often not even the most important metric that determines if an insider transaction is significant.

In insider purchases, Regals Capital Management, a beneficiary owner of Legend International Holdings (PINK:LGDI), bought $2,250,000 worth of company stock. Legend International is a development stage company that explores, develops, and mines base metal properties in Australia. Felix Baker, a Director of molecular diagnostics company Genomic Health (NASDAQ:GHDX), bought $1,363,579 worth of company stock. At publicly owned investment management company Calamos Asset Management (NASDAQ:CLMS), Founder, Chairman, and CEO John Calamos bought $651,102 worth of company stock. Darren Jackson, a Director of Fastenal Company (NASDAQ:FAST), which is a wholesaler and retailer of construction and industrial supplies, bought $528,680 worth of company stock.

In insider sales, Vincent Ryan, a Director of information management company Iron Mountain (NYSE:IRM), sold $17,755,412 worth of company stock. At publicly traded insurance broker Willis Group Holdings (NYSE:WSH), Director Joseph Plumeri sold $12,964,320 worth of company stock. Brown and Williamson, a beneficiary owner of tobacco company Reynolds American (NYSE:RAI). sold $11,376,641 worth of company stock. Reynolds American was created in 2004 when Brown and Williamson, then a controversial company due to claims that it added chemicals to its cigarettes to heighten addictive qualities, merged with R.J. Reynolds. At real estate information marketplace company Zillow (NASDAQ:Z), Co-Founder, Vice Chairman, and President Lloyd Frink sold $10,679,103 worth of company stock while Chairman Richard Barton sold $3,722,968 worth of company stock.

At InsiderInsights.com, we find new investment ideas just about every day using these and more intricate insider screens to determine where we should focus our subsequent fundamental and technical analysis. And while stocks don't (or shouldn't) move up or down based on insider activity alone, insiders tend to be good indicators of when real stock-moving events like earnings surprises, corporate actions, and new products may be in the offing.

Insider Purchases

#:	Filer Name	Insider Titles	Company Name	Ticker	Trans Type	Dollar Value
1	Regals Capital Mgt	BO	Legend Intl	LGDI	JB*	$2,250,000
2	Baker Felix	DIR,BO	Genomic Health	GHDX	B	$1,363,579
3	Calamos John P Sr	CB,CEO,BO	Calamos Asset Mgt	CLMS	B	$651,102
4	RGM Capital	BO	Support Com	SPRT	B	$608,245
5	Frost Phillip MD	CEO,CB,BO	Opko Health	OPK	B	$585,484
6	Jackson Darren R	DIR	Fastenal	FAST	B	$528,680
7	Chung Paul W	VP,GC,SEC	Targa Resources	NGLS	B	$308,551
8	Del Guercio Joseph	DIR	Cytomedix	CMXI	JB*	$280,000
9	Pennant Capital Mgt	BO	Universal Stainless	USAP	B	$158,049
10	Kelliher James F	CFO,TR	Logmein	LOGM	B	$135,320

Source: InsiderInsights.com | Key to Insider Title and Trans Type Codes

Insider Sales

#:	Filer Name	Insider Titles	Company Name	Ticker	Trans Type	Dollar Value
1	Ryan Vincent J	DIR	Iron Mountain	IRM	AS	$17,755,412
2	Mastercard Fdn	BO	Mastercard	MA	S	$12,964,320
3	Plumeri Joseph J	DIR	Willis	WSH	S	$11,530,951
4	Brown & Williamson	BO	Reynolds American	RAI	JS*	$11,376,641
5	Frink Lloyd D	VCB,PR,BO	Zillow	Z	S	$10,679,103
6	Noell Charles III	DIR	Servicenow	NOW	S	$6,013,989
7	Chapman John	DIR	Kapstone Paper	KS	S	$4,390,737
8	Henry Brian C	VP,CFO	CRAY	CRAY	S	$4,374,592
9	Nelson Zachary	PR,CEO,DIR	Netsuite	N	AS	$4,192,493
10	Barton Richard N	CB,DIR,BO	Zillow	Z	S	$3,722,968

Source: InsiderInsights.com | Key to Insider Title and Trans Type Codes

Editor's note: Jonathan Moreland is the founder of Insider Insights and author of "Profit From Legal Insider Trading."