Contingencies (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2008	Dec. 31, 2007	Dec. 31, 2005	Dec. 31, 1997	Sep. 30, 2008	Dec. 31, 2003	Dec. 31, 1993
Loss Contingencies [Line Items]
investment in Trojan								87.00%
Refund to customers for Trojan Investment including interest						$ 33,100,000
Class action damages sought							260,000,000
Site Contingency, Names of Other Potentially Responsible Parties	100		6	14	69
Low estimate of range of cost of Portland Harbor cleanup in total	169,000,000
Upper estimated range of total cost of Portland harbor cleanup	1,800,000,000
Repayments of Pollution Control Bond		$ 5,800,000