SCHEDULE 13G

Amendment No. 1
Russel Metals Inc.
Common Stock
Cusip #781903604


Cusip #781903604
Item 1:	Reporting Person - FMR Corp.
Item 4:	Delaware
Item 5:	0
Item 6:	0
Item 7:	1,410,000
Item 8:	0
Item 9:	1,410,000
Item 11:	2.788%
Item 12:	    HC


Cusip #781903604
Item 1:	Reporting Person - Edward C. Johnson 3d
Item 4:	United States of America
Item 5:	0
Item 6:	0
Item 7:	1,410,000
Item 8:	0
Item 9:	1,410,000
Item 11:	2.788%
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:

		Russel Metals Inc.

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

		1900 Minnesota Court
		Suite 210
		Mississiauga, Ontario  L5N 3C9
		Canada

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:

		781903604

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:	1,410,000

	(b)	Percent of Class:	2.788%

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

	(i)	sole power to vote or to direct
the vote:	0

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

	(iii)	sole power to dispose or to
direct the disposition of:	1,410,000

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



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

	If this statement is being filed to report the fact that as of the
date hereof, the reporting person has ceased to be the
beneficial owner of more than five percent of the class of
securities, check the following (X).

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

	Not applicable

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

	See attached Exhibit A.

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.

	Inasmuch as the reporting persons are no longer the beneficial
owners of more than five percent of the number of shares
outstanding, the reporting persons have no further reporting
obligation under Section 13(d) of the Securities and Exchange
Commission thereunder, and the reporting persons have no
obligation to amend this Statement if any material change
occurs in the facts set forth herein.

Signature

	After reasonable inquiry and to the best of my knowledge and
belief, I certify that the information set forth in this statement
is true, complete and correct.

September 12, 2005
Date

/s/Joseph Mari
Signature

Joseph Mari
Duly authorized under Power of Attorney
dated September 9, 2005, by Eric D. Roiter 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 1,410,000 shares or 2.788%
of the Common Stock outstanding of Russel Metals Inc.  ("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 Russel Metals Inc. owned by the
investment companies at August 31, 2005 included 25,000
shares of Common Stock resulting from the assumed
conversion of 25,000 shares of RUSSEL METALS INC 144A
(1 shares of Common Stock for each share of Convertible
Preferred Stock).

	Edward C. Johnson 3d and FMR Corp., through its
control of Fidelity, and the funds each has sole power to
dispose of the 1,410,000 shares owned by the Funds.

	Members of the family of Edward C. Johnson 3d,
Chairman of FMR Corp., are the predominant owners, directly
or through trusts, of Series B shares of common stock of FMR
Corp., representing 49% of the voting power of FMR Corp.
The Johnson family group and all other Series B shareholders
have entered into a shareholders' voting agreement under
which all Series B shares will be voted in accordance with the
majority vote of Series 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.

	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.



	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 September 12, 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 Russel Metals Inc. at August 31, 2005.

	FMR Corp.

	By /s/ Joseph Mari
	Joseph Mari
	Duly authorized under Power of Attorney dated
September 9, 2005, by Eric D. Roiter by and on behalf of
FMR Corp. and its direct and indirect subsidiaries

	Edward C. Johnson 3d

	By /s/ Joseph Mari
	Joseph Mari
	Duly authorized under Power of Attorney dated
September 9, 2005, by Eric D. Roiter by and on behalf of
Edward C. Johnson 3d

	Fidelity Management & Research Company

	By /s/ Joseph Mari
	Joseph Mari
	Duly authorized under Power of Attorney dated
September 9, 2005, by Eric D. Roiter Secretary