XML 24 R55.htm IDEA: XBRL DOCUMENT v2.4.1.9

Company's Liability for Environmental Obligations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Environmental Exit Cost [Line Items]
Beginning Balance	$ 14.8utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance	$ 14.8utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance
Additions	1.3us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses	0.6us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses
Less: Payments / Reductions	10.6us-gaap_AccrualForEnvironmentalLossContingenciesPayments	0.6us-gaap_AccrualForEnvironmentalLossContingenciesPayments
Less: Current Portion	3.5us-gaap_AccruedEnvironmentalLossContingenciesCurrent	1.0us-gaap_AccruedEnvironmentalLossContingenciesCurrent
Ending Balance	2.0utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance	13.8utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance
Adjustment
Environmental Exit Cost [Line Items]
Ending Balance	5.5utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember	14.8utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember
Fitchburg Gas and Electric Light Company
Environmental Exit Cost [Line Items]
Beginning Balance	12.0utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember	12.0utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember
Additions		0.2us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember
Less: Payments / Reductions	10.1us-gaap_AccrualForEnvironmentalLossContingenciesPayments / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember	0.2us-gaap_AccrualForEnvironmentalLossContingenciesPayments / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember
Less: Current Portion	1.9us-gaap_AccruedEnvironmentalLossContingenciesCurrent / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember
Ending Balance		12.0utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember
Fitchburg Gas and Electric Light Company | Adjustment
Environmental Exit Cost [Line Items]
Ending Balance	1.9utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember	12.0utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_FitchburgGasAndElectricLightCompanyMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember
Northern Utilities Inc
Environmental Exit Cost [Line Items]
Beginning Balance	2.8utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember	2.8utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember
Additions	1.3us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember	0.4us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember
Less: Payments / Reductions	0.5us-gaap_AccrualForEnvironmentalLossContingenciesPayments / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember	0.4us-gaap_AccrualForEnvironmentalLossContingenciesPayments / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember
Less: Current Portion	1.6us-gaap_AccruedEnvironmentalLossContingenciesCurrent / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember	1.0us-gaap_AccruedEnvironmentalLossContingenciesCurrent / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember
Ending Balance	2.0utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember	1.8utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember
Northern Utilities Inc | Adjustment
Environmental Exit Cost [Line Items]
Ending Balance	$ 3.6utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember	$ 2.8utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance / dei_LegalEntityAxis = utl_NorthernUtilitiesIncMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioAdjustmentMember

X

- Definition

The aggregate amount disbursed during the reporting period to settle environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 5.Y.Q2)

-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesPayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The amount added to the accrual for newly incurred environmental loss contingencies. These additions include remediation expense and interest accretion. These additions do not relate to changes in the environmental accrual related to a business acquisition or divestiture, to currency movements, or revisions in previously existing estimates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 5.Y.Q2)

-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

- Details

Name:	us-gaap_EnvironmentalExitCostLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Accrued Environmental Loss Contingencies Current Beginning Balance

+ References

No definition available.

+ Details

Name:	utl_AccruedEnvironmentalLossContingenciesCurrentBeginningBalance
Namespace Prefix:	utl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Accrued Environmental Loss Contingencies, Noncurrent Ending Balance

+ References

No definition available.

+ Details

Name:	utl_AccruedEnvironmentalLossContingenciesNoncurrentEndingBalance
Namespace Prefix:	utl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	dei_LegalEntityAxis=utl_FitchburgGasAndElectricLightCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=utl_NorthernUtilitiesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: