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Environmental matters (Details 2) - USD ($) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 | Jan. 06, 2017
Portland Harbor Site [Member] |  |
Site Contingency [Line Items] |  |
Environmental matters investigative costs | $ 100,000,000 |
Environmental matters, estimated costs |  | $ 1,000,000,000
Eugene, OR Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Total estimated costs for site remediation | 3,500,000 |
Incurred costs for site remediation | $ 320,000 |
Percent of ongoing costs paid | 50.00% |
Estimated proportional share of cleanup liability | 50.00% |
Environmental matters accrual for site remediation | $ 1,600,000 |
Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Environmental matters accrual for site remediation | 6,400,000 |
Total estimated costs for site remedial investigation and feasibility study | 7,600,000 |
Incurred costs for site remedial investigation and feasibility study | 700,000 |
Environmental matters accrual of investigative costs | 6,900,000 |
Bellingham, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | 8,000,000.0 |
Minimum [Member] | Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | 340,000 |
Maximum [Member] | Bremerton, WA Manufactured Gas Plant Site [Member] |  |
Site Contingency [Line Items] |  |
Site contingency, loss exposure not accrued, best estimate | $ 6,400,000 |

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- Definition Best estimate of the loss exposure for reasonably possible environmental contingencies at an individual site for which no accrual has been recorded. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 10 -Subparagraph (c),(d)(2) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859 + Details
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