The amount of retirees and beneficiaries impacted by the purchase of an irrevocable group annuity contract.

No definition available.

Name:	ghc_DefinedBenefitPlanSettlementNumberofRetireesAndBeneficiaries
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Target allocation maximum percentage of investment in a single equity security to total plan assets without prior approval of plan administrator.

+ References

No definition available.

+ Details

Name:	ghc_DefinedBenefitPlanTargetAllocationPercentageOfAssetsSingularEquitySecurityLimitWithoutApprovalOfPlanAdministrator
Namespace Prefix:	ghc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The net periodic benefit or expense for defined benefit pension plans excluding the early retirement program and special separation benefit expense, curtailment, settlement and other programs separately disclosed in the financial statements.

+ References

No definition available.

+ Details

Name:	ghc_NetPeriodicBenefitForDefinedBenefitPensionPlansExcludingEarlyRetirementProgramSpecialSeparationBenefitExpenseCurtailmentAndSettlement
Namespace Prefix:	ghc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of investment companies actively managing plan assets.

+ References

No definition available.

+ Details

Name:	ghc_NumberOfInvestmentCompaniesManagingPlanAssets
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number Of Investments The Companys Pension Plan Held Which Individually Exceed 10 Percent Of Total Plan Assets

+ References

No definition available.

+ Details

Name:	ghc_NumberOfInvestmentsCompanysPensionPlanHeldWhichIndividuallyExceed10PercentOfTotalPlanAssets
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of multiemployer pension plans to which the Company contributed.

+ References

No definition available.

+ Details

Name:	ghc_NumberOfMultiemployerPlansContributedTo
Namespace Prefix:	ghc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of plan assets managed by investment companies.

+ References

No definition available.

+ Details

Name:	ghc_PercentOfPlanAssetsManagedByInvestmentCompanies
Namespace Prefix:	ghc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of plan assets managed internally by the Company.

+ References

No definition available.

+ Details

Name:	ghc_PercentofPlanAssetsManagedInternallybyCompany
Namespace Prefix:	ghc_
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:	ghc_RetirementBenefitsDisclosureLineItems
Namespace Prefix:	ghc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13531-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13537-108611

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

+ Details

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

- Definition

Amount of payment, which decreases benefit obligation of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. Excludes decreases to benefit obligation for remeasurement due to settlement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

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

- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(ii)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

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

- Definition

Amount of cost of providing special or contractual termination benefits payable from defined benefit plan.

+ References

+ Details

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

- Definition

Description of direction and pattern of change in assumed health care cost trend rate used to measure expected cost of benefits for defined benefit postretirement plan.

+ References

No definition available.

+ Details

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

- Definition

Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year.

+ References

+ Details

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

- Definition

Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

+ Details

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

- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=109237824&loc=SL108413299-114919

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of (increase) decrease to benefit obligation of defined benefit plan from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Includes, but is not limited to, lump-sum cash payment to participant in exchange for right to receive specified benefits, purchase of nonparticipating annuity contract and change from remeasurement.

+ References

+ Details

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

- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Year ultimate health care cost trend rate is expected to be reached, in CCYY format.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanYearHealthCareCostTrendRateReachesUltimateTrendRate
Namespace Prefix:	us-gaap_
Data Type:	us-types:gYearListItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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

- Definition

Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(h))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

- Definition

Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 35
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=29639808&loc=d3e29008-114946

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947

+ Details

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

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TransactionTypeAxis=ghc_IrrevocableGroupAnnuityContractPurchaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_DefinedBenefitPlanHealthCareCostTrendGroupsAxis=ghc_PreAge65Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_DefinedBenefitPlanHealthCareCostTrendGroupsAxis=ghc_PostAge65Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_DefinedBenefitPlanHealthCareCostTrendGroupsAxis=ghc_MedicareAdvantageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_PrivateEquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=ghc_SingleEquityConcentrationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=ghc_DefinedBenefitPlanAssetsTotalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=ghc_ConcentrationInSingleEntityTypeOfIndustryForeignCountryOrIndividualFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ghc_EducationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_EarlyRetirmentProgramExpenseAxis=ghc_SeparationIncentiveProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ghc_EducationCode3AndDecileMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_InvestmentManagersAxis=ghc_InvestmentManager1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=ghc_AlphabetAndBerkshireHathawayCommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=ghc_ForeignInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghc_InvestmentManagersAxis=ghc_InvestmentManager2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=ghc_BerkshireHathawayCommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Pensions and Other Postretirement Plans (Narrative) (Details)	1 Months Ended	2 Months Ended	3 Months Ended				10 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($) Investment retirees_beneficiaries	Dec. 31, 2018	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 31, 2018	Dec. 31, 2020 USD ($) Investment multiemployer_plan country	Dec. 31, 2019 USD ($) multiemployer_plan Investment	Dec. 31, 2018 USD ($) multiemployer_plan
Retirement Benefits Disclosure [Line Items]
Special separation benefit expense								$ 13,781,000
Number of multiemployer plans contributed to \| multiemployer_plan								1	1	1
Contributions to multiemployer pension plans								$ 100,000	$ 100,000	$ 100,000
Expense associated with the retirement benefits provided under incentive savings plans								8,800,000	9,800,000	8,600,000
Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Settlement of obligation								0	235,544,000
Settlement						$ 26,900,000		0	91,676,000	26,917,000
Special separation benefit expense								13,781,000	6,432,000	0
Accumulated benefit obligation	$ 991,100,000							1,064,300,000	991,100,000
Company contributions								0	0
Estimated employer contributions in next fiscal year								0
Net Periodic Cost (Benefit) for the Year								(55,354,000)	(52,665,000)	(74,031,000)
Curtailment								$ 0	$ 0	806,000
Percent of Plan Assets Managed Internally by Company								40.00%
Percent Of Plan Assets Managed By Investment Companies								60.00%
Number of investment companies actively managing plan assets \| country								2
Percentage of total plan assets	100.00%							100.00%	100.00%
Pension Plans [Member] \| Irrevocable Group Annuity Contract Purchase [Member]
Retirement Benefits Disclosure [Line Items]
Payment for settlement	$ 216,800,000
Settlement of obligation	$ 212,100,000
Number of retirees and beneficiaries \| retirees_beneficiaries	3,800
Settlement	$ 91,700,000
Supplemental Executive Retirement Plan (SERP) [Member]
Retirement Benefits Disclosure [Line Items]
Accumulated benefit obligation	$ 114,800,000							$ 121,700,000	$ 114,800,000
Company contributions								5,974,000	7,071,000
Other Postretirement Plans [Member]
Retirement Benefits Disclosure [Line Items]
Company contributions								405,000	750,000
Net Periodic Cost (Benefit) for the Year								(4,362,000)	(11,434,000)	(3,679,000)
Curtailment								$ 0	$ 0	$ 3,380,000
Discount rate to determine benefit obligation	2.68%							1.78%	2.68%
Discount rate to determine periodic cost		4.04%					3.11%	2.68%	3.69%
Other Postretirement Plans [Member] \| Pre-Age 65 [Member]
Retirement Benefits Disclosure [Line Items]
Assumed health care cost trend rate								6.59%
Direction of change for assumed health care cost trend rate								decreasing
Ultimate health care cost trend rate								4.50%
Year that rate reaches ultimate trend rate								2029
Other Postretirement Plans [Member] \| Post-Age 65 [Member]
Retirement Benefits Disclosure [Line Items]
Assumed health care cost trend rate								7.01%
Direction of change for assumed health care cost trend rate								decreasing
Ultimate health care cost trend rate								4.50%
Year that rate reaches ultimate trend rate								2029
Other Postretirement Plans [Member] \| Medicare Advantage [Member]
Retirement Benefits Disclosure [Line Items]
Assumed health care cost trend rate								8.25%
Direction of change for assumed health care cost trend rate								decreasing
Ultimate health care cost trend rate								4.50%
Year that rate reaches ultimate trend rate								2029
Private investment fund [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Percentage of total plan assets	7.00%							18.00%	7.00%
Single Equity Concentration [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator								10.00%	10.00%
Value of investments	$ 704,800,000							$ 850,600,000	$ 704,800,000
Percentage of total plan assets	30.00%							30.00%	30.00%
Single Equity Concentration [Member] \| Equity securities [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets \| Investment	1							1	1
Single Equity Concentration [Member] \| Private investment fund [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets \| Investment								1
Single Equity Concentration [Member] \| Equity funds [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets \| Investment	1								1
Defined Benefit Plan Assets Total [Member] \| Concentration In Single Entity, Type Of Industry, Foreign Country Or Individual Fund [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Minimum percentage of plan assets considered as significant concentrations in pension plans								10.00%
Education [Member] \| Separation Incentive Program [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Special separation benefit expense			$ 7,800,000		$ 6,400,000
Education Code3 And Decile [Member] \| Separation Incentive Program [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Special separation benefit expense				$ 6,000,000.0
Investment Manager 1 [Member] \| Alphabet And Berkshire Hathaway Common Stock [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator								15.00%
Investment Manager 1 [Member] \| Maximum [Member] \| Foreign Investments [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets								30.00%
Investment Manager 2 [Member] \| Berkshire Hathaway Common Stock [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator								20.00%
Investment Manager 2 [Member] \| Maximum [Member] \| Foreign Investments [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets								15.00%
Investment Manager 2 [Member] \| Minimum [Member] \| Fixed income securities [Member] \| Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets								10.00%