Enviromental matters (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2012
Portland Harbor site [Member]
Site contingency [Line Items]
Estimated investigative costs	$ 70,000,000
Environmental litigation number 1 [Member]
Site contingency [Line Items]
Site contingency, loss exposure, low estimate	500,000
Site contingency, loss exposure, high estimate	11,000,000
Estimated proportional share of cleanup liability	50.00%
Accrual for environmental loss contingencies	1,200,000
Environmental litigation number 2 [Member]
Site contingency [Line Items]
Site contingency, loss exposure, low estimate	340,000
Site contingency, loss exposure, high estimate	6,400,000
Accrual for environmental loss contingencies	6,400,000
Estimated investigative costs	4,900,000
Environmental litigation number 3 [Member]
Site contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	$ 8,000,000