XML 106 R92.htm IDEA: XBRL DOCUMENT v3.20.4

Commitments and Contingencies - Additional Information (Detail) - Environmental Matters $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) facilities	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Contingencies And Commitments [Line Items]
Pretax charge to comply U.S. federal, state and local environmental control and protection regulations	$ 16.3	$ 15.9	$ 14.7
Capital expenditure to comply environmental regulations	1.2	1.4	$ 1.7
Environmental reserves	91.3	90.8
Environmental reserves included in current liabilities	$ 7.1	10.4
Nuclear Operations Group
Contingencies And Commitments [Line Items]
Number of facilities | facilities	2
Financial assurance to pay expected cost of decommissioning	$ 61.8
Nuclear Energy Group
Contingencies And Commitments [Line Items]
Financial assurance to pay expected cost of decommissioning	$ 47.9	$ 47.0

X

- Definition

Contingencies and commitments line items

+ References

No definition available.

+ Details

Name:	bwxt_ContingenciesAndCommitmentsLineItems
Namespace Prefix:	bwxt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Financial assurance to pay expected cost of decommissioning.

+ References

No definition available.

+ Details

Name:	bwxt_FinancialAssuranceToPayExpectedCostOfDecommissioning
Namespace Prefix:	bwxt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Number of former nuclear fuel processing facilities.

+ References

No definition available.

+ Details

Name:	bwxt_NumberOfFormerNuclearFuelProcessingFacilities
Namespace Prefix:	bwxt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingencies
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 in twelve months or in the next operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6911-107765

+ Details

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

X

- Definition

Amount of environmental remediation costs capitalized. These expenditures may relate to long-lived improvements in operating facilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 25
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=39739230&loc=d3e11660-110855

+ Details

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

X

- Definition

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109237650&loc=d3e13064-110858

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859

+ Details

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

X

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=bwxt_EnvironmentalMattersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

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