License and Other Agreements (Details) - USD ($) $ in Thousands	1 Months Ended
Mar. 31, 2018	Jan. 31, 2018
Catalent Agreement \| Collaborative arrangement
License and other agreements
Last patent right expiration period		10 years
Automatic extension period		1 year
Catalent Agreement \| Collaborative arrangement \| Maximum
License and other agreements
Milestone payment to be paid		$ 1,500
BMS Agreement
License and other agreements
Upfront payment under the BMS Amendment	$ 50,000

- Definition

Represents information pertaining to the automatic extension of the license agreement unless either party gives notice of intent to terminate.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Represents information pertaining to the equity method period of time that shares will be purchased after the initial closing.

+ References

No definition available.

+ Details

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

- 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

- Details

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

- Details

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

- Details

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

- Details

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