Represents information pertaining to the equity method shares to be purchased in four equal tranches.

No definition available.

Name:	bhvn_EquityMethodEqualTranchesOfCommonStockPurchasedPerAgreement
Namespace Prefix:	bhvn_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents information pertaining to the price per share of the stock purchased from equity investment.

+ References

No definition available.

+ Details

Name:	bhvn_EquityMethodPricePerCommonShareOfStockPurchased
Namespace Prefix:	bhvn_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents information pertaining to the shares of stock purchased from equity investment.

+ References

No definition available.

+ Details

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Namespace Prefix:	bhvn_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of agreements

+ References

No definition available.

+ Details

Name:	bhvn_NumberOfAgreements
Namespace Prefix:	bhvn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Face amount or stated value per share of common stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

+ Details

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

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Subsequent Events (Details) $ / shares in Units, $ in Thousands			1 Months Ended		9 Months Ended
	Oct. 05, 2017 USD ($) agreement $ / shares shares	Oct. 05, 2017 USD ($) agreement $ / shares shares	Jun. 30, 2017 USD ($) shares	Mar. 31, 2017 USD ($) shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Oct. 31, 2017 shares	May 31, 2017 $ / shares	Dec. 31, 2016 $ / shares	Aug. 29, 2016 $ / shares shares
Subsequent Events
Common stock, par value (in dollars per share) \| $ / shares								$ 0	$ 0
Cash payment for purchase of equity method investment \| $					$ 2,999	$ 3,000
Kleo
Subsequent Events
Shares purchased in equal tranches			1,375,000	1,375,000						1,375,000
Shares of Kleo common stock purchased										3,000,000
Price per share \| $ / shares										$ 1.00
Cash payment for purchase of equity method investment \| $			$ 1,375	$ 1,375	$ 3,351
Ownership percentage					33.00%				18.60%
Kleo \| Subsequent Event
Subsequent Events
Shares purchased in equal tranches	1,375,000	1,375,000
Common stock, par value (in dollars per share) \| $ / shares	$ 0.0001	$ 0.0001
Number of agreements \| agreement	2	2
Shares of Kleo common stock purchased							3,424,543
Cash payment for purchase of equity method investment \| $		$ 1,375
Ownership percentage	43.30%	43.30%					43.30%
Kleo \| First Subscription Agreement \| Subsequent Event
Subsequent Events
Shares of Kleo common stock purchased	1,397,904	1,397,904
Price per share \| $ / shares	$ 1.0993	$ 1.0993
Cash payment for purchase of equity method investment \| $	$ 1,537	$ 1,537
Kleo \| Second Subscription Agreement \| Subsequent Event
Subsequent Events
Shares of Kleo common stock purchased	651,639	651,639
Price per share \| $ / shares	$ 1.0993	$ 1.0993
Cash payment for purchase of equity method investment \| $	$ 716	$ 716