XML 110 R96.htm IDEA: XBRL DOCUMENT
v3.20.4

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Foreign Exchange Contracts |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of foreign currency forward contracts | $ (2.2) | $ (0.8)
Senior Notes Due 2026 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of senior notes | 415.5 | 423.5
Senior Notes Due 2028 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of senior notes | $ 416.7 | $ 416.7

X
- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
Name: | us-gaap_LongTermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=bwxt_SeniorNotesDue2026Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=bwxt_SeniorNotesDue2028Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |