Agreement, Initial Term

No definition available.

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

- Definition

Eligible Milestone Payments, Commercial

+ References

No definition available.

+ Details

Name:	bhvn_EligibleMilestonePaymentsCommercial
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Eligible Milestone Payments, Development

+ References

No definition available.

+ Details

Name:	bhvn_EligibleMilestonePaymentsDevelopment
Namespace Prefix:	bhvn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

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

+ References

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

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

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

License and Other Agreements - Moda Pharmaceuticals LLC (Details) - USD ($) $ in Thousands		3 Months Ended
	Jan. 01, 2021	Mar. 31, 2021	Mar. 31, 2020
License and other agreements
Payment for license agreement		$ 0	$ 20,750
Issuance of common shares as payment for assets		$ 10,243
Moda Pharmaceuticals LLC \| Moda Agreement
License and other agreements
Eligible development milestone payments	$ 81,612
Eligible commercial milestone payments	$ 30,171
Initial term of agreement (in years)	4 years
Moda Pharmaceuticals LLC \| Moda Agreement \| License agreement
License and other agreements
Payment for license agreement	$ 2,700
Issuance of common shares as payment for assets (in shares)	37,836
Issuance of common shares as payment for assets	$ 3,243