Financial Instruments and Concentration of Risk (Fair Values of Derivative Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Fair Value of Derivative Assets	$ 2,952	$ 2,409
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Value of Derivative Assets	2,952	2,409
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Value of Derivative Assets	0	480
Other non-current assets [Member] | Derivatives designated as hedging instruments [Member] | Interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Value of Derivative Assets	2,952	2,409
Other current assets | Derivatives not designated as hedging instruments [Member] | Lumber contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Value of Derivative Assets	$ 0	$ 480