XML 101 R87.htm IDEA: XBRL DOCUMENT v3.20.4

Capital Stock - Additional Information (Detail) - USD ($)			1 Months Ended	12 Months Ended
	Nov. 06, 2018	Feb. 24, 2017	Oct. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Capital Stock [Line Items]
Additional common stock at an aggregate purchase price		$ 150,000,000	$ 300,000,000
Common stock repurchased				$ 27,288,000	$ 30,369,000	$ 222,986,000
Share Repurchase Program
Capital Stock [Line Items]
Additional common stock at an aggregate purchase price	$ 250,000,000			$ 22,000,000.0	$ 20,000,000.0
Common stock repurchased (shares)				338,521	443,877	4,523,934
Common stock repurchased						$ 214,700,000
Stock repurchase program, remaining authorized repurchase amount				$ 143,400,000
Stock repurchase program, term	3 years

X

- Definition

Capital Stock [Line Items]

+ References

No definition available.

+ Details

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

X

- Definition

Stock repurchase program additional authorized amount for share repurchase program.

+ References

No definition available.

+ Details

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

X

- Definition

Period which shares may be purchased under a stock repurchase plan authorized by an entity's Board of Directors, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramPeriodInForce1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount remaining of a stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 3: 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(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

+ Details

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

X

- Details

Name:	us-gaap_ShareRepurchaseProgramAxis=bwxt_ShareRepurchaseProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: