Enviromental matters (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013
Portland Harbor Site [Member]
Site Contingency [Line Items]
Environmental matters investigative costs	$ 70,000,000
Environmental litigation number 1 [Member]
Site Contingency [Line Items]
Site contingency, high estimate, loss exposure	11,000,000
Estimated proportional share of cleanup liability	50.00%
Accrual for environmental loss contingencies	1,300,000
Site contingency, low estimate, loss exposure	500,000
Environmental litigation number 2 [Member]
Site Contingency [Line Items]
Site contingency, high estimate, loss exposure	6,400,000
Environmental matters investigative costs	6,700,000
Accrual for environmental loss contingencies	6,400,000
Site contingency, low estimate, loss exposure	340,000
Environmental litigation number 3 [Member]
Site Contingency [Line Items]
Site contingency, loss exposure not accrued, best estimate	8,000,000
Environmental litigation number 4 [Member]
Site Contingency [Line Items]
Loss contingency, damages paid, value	$ 100,000