SCHEDULE 13G

Amendment No. 1
Simpson Manufacturing Co
Common Stock
Cusip #829073105

Cusip #829073105
Item 1:	Reporting Person - FMR Corp.
Item 4:	Delaware
Item 5:	585,830
Item 6:	0
Item 7:	5,396,566
Item 8:	0
Item 9:	5,396,566
Item 11:	11.218%
Item 12:	    HC

Cusip #829073105
Item 1:	Reporting Person - Edward C. Johnson 3d
Item 4:	United States of America
Item 5:	0
Item 6:	0
Item 7:	5,396,566
Item 8:	0
Item 9:	5,396,566
Item 11:	11.218%
Item 12:	IN



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

This filing has been made to amend a previous filing made as of August 31,
2006, in order to include the Issuers Principal Executive Offices address.


Item 1(a).	Name of Issuer:

		Simpson Manufacturing Co

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

		5956 West Las Positas Boulevard
		Pleasanton, CA  94588


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:

		829073105

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:	5,396,566

(b)	Percent of Class:	11.218%

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

	(i)  sole power to vote or to direct the vote: 585,830

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

	(iii)  sole power to dispose or to direct the disposition of: 5,396,566

	(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 Simpson Manufacturing Co.  The interest of one person, Fidelity Low Priced
Stock Fund, an investment company registered under the Investment Company Act
of 1940, in the Common Stock of Simpson Manufacturing Co, amounted to
4,810,736 shares or 10.000% of the total outstanding Common Stock at
August 31, 2006.

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.

	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 statement
is true, complete and correct.

September 13, 2006
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 5,105,036 shares or 10.612% of the Common Stock
outstanding of Simpson Manufacturing Co  ("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 ownership of one investment company, Fidelity Low Priced Stock Fund,
amounted to 4,810,736 shares or 10.000% of the Common Stock outstanding.
Fidelity Low Priced Stock Fund has its principal business office at 82
Devonshire Street, Boston, Massachusetts 02109.

Edward C. Johnson 3d and FMR Corp., through its control of Fidelity,
and the funds each has sole power to dispose of the 5,105,036 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.

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  119,030 shares or
0.247% 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 119,030 shares and sole power to vote or to direct the
voting of 119,030 shares of Common Stock owned by the
institutional account(s) as reported above.

Fidelity International Limited ("FIL"), Pembroke Hall, 42 Crow
Lane, Hamilton, Bermuda, and various foreign-based subsidiaries
provide investment advisory and management services to a number of
non-U.S. investment companies and certain institutional investors.
FIL, which is a qualified institution under section 240.13d-1(b)(1)
pursuant to an SEC No-Action letter dated October 5, 2000, is the
beneficial owner of 172,500 shares or 0.359% of the Common Stock
outstanding of the Company.

Partnerships controlled predominantly by members of the family of
Edward C. Johnson 3d, Chairman of FMR Corp. and FIL, or trusts for
their benefit, own shares of FIL voting stock with the right to cast
approximately 47% of the total votes which may be cast by all holders
of FIL voting stock.  FMR Corp. and FIL are separate and independent
corporate entities, and their Boards of Directors are generally
composed of different individuals.

FMR Corp. and FIL are of the view that they are not acting as a
"group" for purposes of Section 13(d) under the Securities Exchange
Act of 1934 (the "1934" Act) and that they are not otherwise required
to attribute to each other the "beneficial ownership" of securities
"beneficially owned" by the other corporation within the meaning of
Rule 13d-3 promulgated under the 1934 Act.  Therefore, they are of
the view that the shares held by the other corporation need not be
aggregated for purposes of Section 13(d). However, FMR Corp. is
making this filing on a voluntary basis as if all of the shares
are beneficially owned by FMR Corp. and FIL on a joint basis.


	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 13, 2006, 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 Simpson Manufacturing Co at August 31, 2006.

	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

	Fidelity Management & Research Company

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

	Fidelity Low Priced Stock Fund

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