SCHEDULE 13G

Amendment No. 4 
Red Hat Incorporated 
Common Stock 
Cusip #756577102 


Cusip #756577102 
Item 1:	Reporting Person - FMR Corp.
Item 4:	Delaware
Item 5:	20,858 
Item 6:	0 
Item 7:	27,233,807 
Item 8:	0 
Item 9:	27,233,807 
Item 11:	14.751% 
Item 12:	    HC


Cusip #756577102  
Item 1:	Reporting Person - Edward C. Johnson 3d 
Item 4:	United States of America
Item 5:	0 
Item 6:	0 
Item 7:	27,233,807 
Item 8:	0 
Item 9:	27,233,807 
Item 11:	14.751% 
Item 12:	IN 


Cusip #756577102 
Item 1:	Reporting Person - Abigail P. Johnson 
Item 4:	United States of America
Item 5:	0 
Item 6:	0 
Item 7:	27,233,807 
Item 8:	0 
Item 9:	27,233,807 
Item 11:	14.751% 
Item 12:	    IN



	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)




Item 1(a).	Name of Issuer:	

		Red Hat Incorporated 

Item 1(b).	Name of Issuer's Principal Executive Offices:

		2600 Meridian Parkway  
		Durham, NC  27713
		  

Item 2(a).	Name of Person Filing: 

		FMR Corp.

Item 2(b).	Address or Principal Business Office or, if None, 
Residence:

		82 Devonshire Street, Boston, 
Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		Common Stock 

Item 2(e).	CUSIP Number:  

		756577102 

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-2(b) 
and the person filing, FMR Corp., is a parent holding company 
in accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See 
Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	27,233,807 

	(b)	Percent of Class:	14.751% 

	(c)	Number of shares as to which such 
person has:  

	(i)	sole power to vote or to direct 
the vote:	20,858 

	(ii)	shared power to vote or to 
direct the vote:	0 

	(iii)	sole power to dispose or to 
direct the disposition of:	27,233,807 

	(iv)	shared power to dispose or to 
direct the disposition of:	0 



Item 5.	Ownership of Five Percent or Less of a Class.

	Not applicable.

Item 6.	Ownership of More than Five Percent on Behalf of Another 
Person.

	Various persons have the right to receive or the power to 
direct the receipt of dividends from, or the proceeds from the 
sale of, the Common Stock of Red Hat Incorporated.  The 
interest of one person, Fidelity Growth Company Fund, an 
investment company registered under the Investment 
Company Act of 1940, in the Common Stock of Red Hat 
Incorporated, amounted to 18,349,401 shares or 9.938% of the 
total outstanding Common Stock at December 31, 2004. 

Item 7.	Identification and Classification of the Subsidiary Which 
Acquired the Security Being Reported on By the Parent 
Holding Company.

	See attached Exhibit(s) A, B. 

Item 8.	Identification and Classification of Members of 
the Group.

	Not Applicable. See attached Exhibit A. 

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	By signing below I certify that, to the best of my knowledge 
and belief, the securities referred to above were acquired in the 
ordinary course of business and were not acquired for the 
purpose of and do not have the effect of changing or 
influencing the control of the issuer of such securities and 
were not acquired in connection with or as a participant in any 
transaction having such purpose or effect.

Signature

	After reasonable inquiry and to the best of my knowledge and 
belief, I certify that the information set forth in this Schedule 
13G in connection with FMR Corp.'s beneficial ownership of 
the Common Stock of Red Hat Incorporated at December 31, 
2004 is true, complete and correct. 

February 14, 2005 			
Date

/s/Eric D. Roiter				
Signature

Eric D. Roiter				
Duly authorized under Power of Attorney
dated December 30, 1997 by and on behalf
of FMR Corp. and its direct and indirect
subsidiaries


	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)



	Pursuant to the instructions in Item 7 of Schedule 
13G, Fidelity Management & Research Company 
("Fidelity"), 82 Devonshire Street, Boston, Massachusetts 
02109, a wholly-owned subsidiary of FMR Corp. and an 
investment adviser registered under Section 203 of the 
Investment Advisers Act of 1940, is the beneficial owner of 
27,212,949 shares or 14.739% of the Common Stock 
outstanding of Red Hat Incorporated  ("the Company") as a 
result of acting as investment adviser to various investment 
companies registered under Section 8 of the Investment 
Company Act of 1940. The number of shares of Common 
Stock of Red Hat Incorporated owned by the investment 
companies at December 31, 2004 included 444,208 shares of 
Common Stock resulting from the assumed conversion of 
$11,368,000 principal amount of RED HAT CV .5% 1/15/24 
144A (39.0753 shares of Common Stock for each $1,000 
principal amount of debenture). The number of shares of 
Common Stock of Red Hat Incorporated owned by the 
investment companies at December 31, 2004 included 
339,330 shares of Common Stock resulting from the assumed 
conversion of $8,684,000 principal amount of RED HAT CV 
.5% 1/15/24 (39.0753 shares of Common Stock for each 
$1,000 principal amount of debenture).

	The ownership of one investment company, Fidelity 
Growth Company Fund, amounted to 18,349,401 shares or 
9.938% of the Common Stock outstanding. Fidelity Growth 
Company Fund has its principal business office at 82 
Devonshire Street, Boston, Massachusetts 02109.

	Edward C. Johnson 3d, FMR Corp., through its 
control of Fidelity, and the funds each has sole power to 
dispose of the 27,212,949 shares owned by the Funds.

	Neither FMR Corp. nor Edward C. Johnson 3d, 
Chairman of FMR Corp., has the sole power to vote or direct 
the voting of the shares owned directly by the Fidelity Funds, 
which power resides with the Funds' Boards of Trustees.  
Fidelity carries out the voting of the shares under written 
guidelines established by the Funds' Boards of Trustees.

	Fidelity Management Trust Company, 82 Devonshire 
Street, Boston, Massachusetts 02109, a wholly-owned 
subsidiary of FMR Corp. and a bank as defined in Section 
3(a)(6) of the Securities Exchange Act of 1934, is the 
beneficial owner of  20,820 shares or 0.011% of the Common 
Stock outstanding of the Company as a result of its serving as 
investment manager of the institutional account(s).

	Edward C. Johnson 3d and FMR Corp., through its 
control of Fidelity Management Trust Company, each has 
sole dispositive power over 20,820 shares and sole power to 
vote or to direct the voting of 20,820 shares of Common 
Stock owned by the institutional account(s) as reported 
above.

	Strategic Advisers, Inc., 82 Devonshire Street, 
Boston, MA 02109, a wholly-owned subsidiary of FMR 
Corp. and an investment adviser registered under Section 203 
of the Investment Advisers Act of 1940, provides investment 
advisory services to individuals.  As such, FMR Corp.'s 
beneficial ownership includes 38 shares, or 0.000%, of the 
Common Stock stock outstanding of Red Hat Incorporated, 
beneficially owned through Strategic Advisers, Inc.

	Members of the Edward C. Johnson 3d family are the 
predominant owners of Class B shares of common stock of 
FMR Corp., representing approximately 49% of the voting 
power of FMR Corp.  Mr. Johnson 3d owns 12.0% and 
Abigail Johnson owns 24.5% of the aggregate outstanding 
voting stock of FMR Corp.  Mr. Johnson 3d is Chairman of 
FMR Corp. and Abigail P. Johnson is a Director of FMR 
Corp.  The Johnson family group and all other Class B 
shareholders have entered into a shareholders' voting 
agreement under which all Class B shares will be voted in 
accordance with the majority vote of Class B shares.  
Accordingly, through their ownership of voting common 
stock and the execution of the shareholders' voting 
agreement, members of the Johnson family may be deemed, 
under the Investment Company Act of 1940, to form a 
controlling group with respect to FMR Corp.

 


	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
	RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on February 14, 2005, agree 
and consent to the joint filing on their behalf of this Schedule 
13G in connection with their beneficial ownership of the 
Common Stock of Red Hat Incorporated at December 31, 
2004.

	FMR Corp.

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of FMR Corp. and its direct and indirect 
	subsidiaries

	Edward C. Johnson 3d

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Edward C. Johnson 3d

	Abigail P. Johnson

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Duly authorized under Power of Attorney
	dated December 30, 1997, by and on behalf
	of Abigail P. Johnson

	Fidelity Management & Research Company

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Senior V.P. and General Counsel

	Fidelity Growth Company Fund

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Secretary