Name:	bhvn_ExpirationPeriodBasedOnCountryByCountryBasisAfterFirstCommercialSale
Namespace Prefix:	bhvn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the change in the fair value of the contingent equity that is recognized as a component of other income.

No definition available.

Name:	bhvn_FairValueAdjustmentOfContingentEquityLiability
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the amount of milestone payment to be paid by the company upon the achievement of specified commercial milestones and annual royalty payments based on net sales of products from patents.

No definition available.

Name:	bhvn_MilestonePaymentToBePaidByCompanyUponSpecifiedCommercialMilestoneAchievement
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

Name:	bhvn_MilestonePaymentToBePaidByCompanyUponSpecifiedRegulatoryAndCommercialMilestoneAchievement
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the amount of milestone payment to be paid by the company upon the achievement of specified regulatory milestones and annual royalty payments based on net sales of products from patents.

No definition available.

Name:	bhvn_MilestonePaymentToBePaidByCompanyUponSpecifiedRegulatoryMilestoneAchievement
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the amount of milestone payment to be paid by the company upon the achievement of specified regulatory milestones and annual royalty payments based on net sales of products from patents other than the specified product.

No definition available.

Name:	bhvn_MilestonePaymentToBePaidByCompanyUponSpecifiedRegulatoryMilestoneAchievementForOtherThanSpecifiedProducts
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

Name:	bhvn_MilestonePaymentToBePaidByCompanyUponSpecifiedSalesBasedMilestoneAchievement
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents information pertaining to the remaining percentage of shares to be issued after specified contractual events.

No definition available.

Name:	bhvn_PercentageOfRemainingSharesIssuedAfterSpecifiedContractualEvents
Namespace Prefix:	bhvn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Represents information pertaining to the percentage of shares to be issued upon the closing of the transaction.

No definition available.

Name:	bhvn_PercentageOfSharesIssuedUponClosingOfTransaction
Namespace Prefix:	bhvn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Represents information pertaining to the right of BMS to purchase fully diluted shares as a percentage.

No definition available.

Name:	bhvn_RightToPurchaseFullyDilutedSharesPercentage
Namespace Prefix:	bhvn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

It represents the common stock value agreed to issue under the agreement.

No definition available.

Name:	bhvn_StockAgreedToIssueDuringPeriodValueNewIssues
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Number of new stock issued during the period classified as temporary equity.

No definition available.

Name:	bhvn_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	bhvn_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.

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

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

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

The cash outflow to acquire asset without physical form usually arising from contractual or other legal rights, excluding goodwill.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

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

The difference between the carrying amount of a financial instrument subject to a registration payment arrangement recorded as temporary equity prior to adoption of FSP EITF 00-19-2 and the carrying amount reclassified to permanent equity upon the adoption of FSP EITF 00-19-2. Recorded as a cumulative effect adjustment to the beginning balance of retained earnings. Does not apply to registration payment arrangements that are no longer outstanding upon adoption of FSP EITF 00-19-2.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=120519210&loc=d3e90193-114008

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section S99
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=65877616&loc=SL6540498-122764

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

Price of a single share of a number of saleable stocks of a company.

No definition available.

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

Number of new stock issued during the period.

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(29))
-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 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

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

Reference 4: 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(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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

Number of shares of stock issued during the period as part of a transaction to acquire assets that do not qualify as a business combination.

No definition available.

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

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

Reference 1: 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 2: 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 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

Reference 4: 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(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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

Value of shares of stock issued during the period as part of a transaction to acquire assets that do not qualify as a business combination.

No definition available.

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

Value of new stock classified as temporary equity issued during the period.

No definition available.

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

Name:	srt_CounterpartyNameAxis=bhvn_AstraZenecaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LicensingAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_TypeOfArrangementAxis=us-gaap_CollaborativeArrangementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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