Related Party Transactions (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	12 Months Ended									1 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Chief Executive Officer	Dec. 31, 2010 Chief Executive Officer	Dec. 31, 2009 Chief Executive Officer	Dec. 31, 2011 Gerald Hagel, vice president and Susan Hagel, spouse Simpson Strong-Tie Y	Dec. 31, 2011 Keymark Enterprises, LLC	Dec. 31, 2010 Keymark Enterprises, LLC	Jan. 31, 2010 Entities related to Keymark Entity	Dec. 31, 2009 Entities related to Keymark Entity	Dec. 31, 2011 Entities related to Keymark	Dec. 31, 2011 Simpson PSB fund
Related Party Transaction
Cost of use of airplanes	$ 508,000	$ 532,000	$ 409,000	$ 30,000	$ 30,000	$ 27,000
Lease agreement, extended period (in years)							5
Annual lease payment to lease the property from Mr. Hagel and his wife Susan Hagel, a former employee of Simpson Strong-Tie	7,300,000	7,100,000	6,600,000				270,000
Fees for software development								2,500,000	800,000
Loans made to related parties		1,798,000	1,204,000					600,000		1,800,000	700,000
Interest rate of loans (as a percent)								7.00%		5.50%	5.50%	5.50%
Number of related entities										2	2
Ownership interest given up in exchange for software assets acquired (as a percent)								46.10%
Number of shares purchased													125
Value of shares purchased													$ 3,500,000
Shares purchased, price per share (in dollars per share)													$ 27.6