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, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Chief Executive Officer	Dec. 31, 2011 Chief Executive Officer	Dec. 31, 2010 Chief Executive Officer	Dec. 31, 2012 Gerald Hagel, vice president and Susan Hagel, spouse Simpson Strong-Tie	Dec. 31, 2011 Keymark Enterprises, LLC	Jan. 31, 2013 Entities related to Keymark	Jul. 31, 2012 Entities related to Keymark	Jan. 31, 2010 Entities related to Keymark item	Dec. 31, 2009 Entities related to Keymark item	Dec. 31, 2011 Simpson PSB fund
Related Party Transaction
Cost of use of airplanes	$ 500,000	$ 500,000	$ 500,000	$ 20,000	$ 30,000	$ 30,000
Annual lease payment to lease the property from Mr. Hagel and his wife Susan Hagel, a former employee of Simpson Strong-Tie	6,900,000	7,300,000	7,100,000				300,000
Loans made to related parties			(1,798,000)								(1,700,000)	(700,000)
Number of related entities											2	2
Interest rate of loans (as a percent)											5.50%	5.50%
Loan repayments by related parties	1,698,000	552,000	50,000						700,000	1,700,000
Fees for software development								2,500,000
Software assets acquired								11,500,000
Software assets acquired, net cash payments								6,200,000
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)													$ 27.60