Number of new mechanisms

No definition available.

Name:	psd_Numberofnewmechanisms
Namespace Prefix:	psd_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Public Utilities, Rate Case, Deferred Storm Costs Threshold

+ References

No definition available.

+ Details

Name:	psd_PublicUtilitiesRateCaseDeferredStormCostsThreshold
Namespace Prefix:	psd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Public Utilities, Rate Case, Deferred Storm Qualifying Costs

+ References

No definition available.

+ Details

Name:	psd_PublicUtilitiesRateCaseDeferredStormQualifyingCosts
Namespace Prefix:	psd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities

+ References

No definition available.

+ Details

Name:	psd_RegulatedUtilityAllowedRateOfReturnOnNetRegulatoryAssetsAndLiabilities
Namespace Prefix:	psd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Regulated Utlity, After-tax Allowed Rate of Return on Net Regulatory Assets and Liabilities

+ References

No definition available.

+ Details

Name:	psd_RegulatedUtlityAfterTaxAllowedRateOfReturnOnNetRegulatoryAssetsAndLiabilities
Namespace Prefix:	psd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Storm Damage Costs Deferred During Period

+ References

No definition available.

+ Details

Name:	psd_StormDamageCostsDeferredDuringPeriod
Namespace Prefix:	psd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Storm Damage Costs Incurred During Period

+ References

No definition available.

+ Details

Name:	psd_StormDamageCostsIncurredDuringPeriod
Namespace Prefix:	psd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue recognized that was previously reported as deferred or unearned revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response))
-URI http://asc.fasb.org/extlink&oid=65893310&loc=d3e214044-122780

+ Details

Name:	us-gaap_DeferredRevenueRevenueRecognized1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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

- Definition

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of public utility's requested equity to capital, including debt and equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedEquityCapitalStructurePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of public utility's amended requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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

- Definition

Percentage of public utility's amended requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmendedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of public utility's requested return on equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesRequestedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=psd_ElectricMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=psd_DecouplingMechanismMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=psd_GeneralRateCaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=psd_TaxCutsandJobsActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=psd_ColstripRegulatoryAssetDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Regulation and Rates (Details) $ in Thousands					3 Months Ended		4 Months Ended	12 Months Ended
Regulation and Rates (Details) $ in Thousands	Dec. 29, 2017 USD ($)	Dec. 19, 2017 USD ($)	Jan. 13, 2017	Jan. 01, 2017	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Apr. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2016 USD ($)
Regulatory Assets [Line Items]
Income tax (benefit) expense					$ 11,803	$ 62,543	$ 27,400
Subsidiaries [Member]
Regulatory Assets [Line Items]
Public Utilities, Rate Case, Deferred Storm Costs Threshold									$ 10,000
Public Utilities, Rate Case, Deferred Storm Qualifying Costs									500
Income tax (benefit) expense					21,691	71,798
Subsidiaries [Member] \| Electric [Member]
Regulatory Assets [Line Items]
Storm Damage Costs Incurred During Period					5,700	26,400
Storm Damage Costs Deferred During Period					0	$ 8,800
Public Utilities, Rate Case, Deferred Storm Costs Threshold									$ 8,000
Decoupling Mechanism [Member]
Regulatory Assets [Line Items]
Deferred Revenue, Revenue Recognized								$ 20,800
Decoupling Mechanism [Member] \| Subsidiaries [Member] \| Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage				2.20%
Decoupling Mechanism [Member] \| Subsidiaries [Member] \| Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage				3.00%
Decoupling Mechanism [Member] \| Maximum [Member] \| Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage		5.00%
Decoupling Mechanism [Member] \| Maximum [Member] \| Subsidiaries [Member]
Regulatory Assets [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage		3.00%
Decoupling Mechanism [Member] \| Maximum [Member] \| Subsidiaries [Member] \| Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage		3.00%
General Rate Case [Member] \| Subsidiaries [Member]
Regulatory Assets [Line Items]
Number of new mechanisms			2
Regulated Utility, Allowed Rate of Return on Net Regulatory Assets and Liabilities		7.60%
Regulated Utility, After-tax Allowed Rate of Return on Net Regulatory Assets and Liabilities		6.55%
Public Utilities, Requested Equity Capital Structure, Percentage		48.50%
Public Utilities, Requested Return on Equity, Percentage		9.50%
General Rate Case [Member] \| Subsidiaries [Member] \| Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount		$ (35,500)
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage		(3.80%)
General Rate Case [Member] \| Subsidiaries [Member] \| Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount		$ 20,200
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage		0.90%
Tax Cuts and Jobs Act [Member] \| Subsidiaries [Member] \| Natural Gas [Member]
Regulatory Assets [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ (23,600)
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage	(3.00%)
Tax Cuts and Jobs Act [Member] \| Subsidiaries [Member] \| Electric [Member]
Regulatory Assets [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ (72,900)
Public Utilities, Requested Rate Increase (Decrease), Amended, Percentage	(3.50%)
Colstrip Regulatory Asset [Domain]
Regulatory Assets [Line Items]
Regulatory Assets					$ 127,800					$ 127,600