XML 27 R43.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Environmental Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  |  |  | 3 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2014 | Dec. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 Northern Utilities Inc | Dec. 31, 2013 Northern Utilities Inc | Mar. 31, 2014 Fitchburg Gas and Electric Light Company Environmental Clean Up Costs | Dec. 31, 2013 Fitchburg Gas and Electric Light Company Environmental Clean Up Costs | Mar. 31, 2014 Fitchburg Gas and Electric Light Company Environmental Restoration Costs | Mar. 31, 2014 New Hampshire Environmental Restoration Costs | Mar. 31, 2014 Maine Environmental Restoration Costs | Mar. 31, 2014 Environmental Matters
Site Contingency [Line Items] |  |  |  |  |  |  |  |  |  |  |
Income (loss) incurred in excess of recorded amount |  |  |  |  |  |  |  |  |  |  | $ 0
Amortization period for environmental costs |  |  |  |  |  |  |  | 7 years | 7 years | 5 years |
Environmental obligations, Current | 1.4 | 1.0 | 1.0 | 0.4 | 1.0 | 1.0 | 0 |  |  |  |
Environmental obligations, Non-current | $ 12.8 | $ 13.8 | $ 13.8 | $ 1.8 | $ 1.8 | $ 11.0 | $ 12.0 |  |  |  |

X
- Definition Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 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 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6911-107765 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 10 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859 + Details
Name: | us-gaap_AccruedEnvironmentalLossContingenciesCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable after twelve months or beyond the next operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 24 -Article 5 Reference 3: 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 4: 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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 10 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859 + Details
Name: | us-gaap_AccruedEnvironmentalLossContingenciesNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_SiteContingencyLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Disclosure that no losses are anticipated exceeding those amounts recorded. + References No definition available. + Details
Name: | utl_ChangeInNetIncomeLossDueToChangeInEstimates
Namespace Prefix: | utl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Remaining Amortization Period. + References No definition available. + Details
Name: | utl_RemainingAmortizationPeriod
Namespace Prefix: | utl_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant