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Environmental matters (Details 2) - USD ($) |  | 9 Months Ended
--- | --- | ---
Oct. 12, 2015 | Sep. 30, 2015
Portland Harbor Site [Member] |  |
Site Contingency [Line Items] |  |
Environmental matters investigative costs |  | $ 70,000,000
Eugene, OR Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, low estimate, loss exposure |  | 500,000
Site contingency, high estimate, loss exposure |  | $ 11,000,000
Estimated proportional share of cleanup liability |  | 50.00%
Accrual for environmental loss contingencies |  | $ 1,700,000
Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, low estimate, loss exposure |  | 340,000
Site contingency, high estimate, loss exposure |  | 6,400,000
Accrual for environmental loss contingencies |  | 12,200,000
Bellingham, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate |  | $ 8,000,000
Subsequent event [Member] | Coos County Oregon [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | $ 160,000 |

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
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