Represents the annual cumulative increase for common stock issuance, as a percentage of the number of shares of common stock issued and outstanding.

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Increase in aggregate number of common shares reserved for future issuance.

+ References

No definition available.

+ Details

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

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

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

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- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

+ 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(28))
-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(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Period Type:

Stock-based Compensation - Employee Stock Purchase Plan (Details) - shares	1 Months Ended	6 Months Ended
	May 31, 2015	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2020
Stock-based compensation
ESPP shares issued during period (in shares)		17,018	10,718
Employee Stock
Stock-based compensation
Number of common shares reserved for future issuance (in shares)	243,347
Annual increase for common stock for issuance (as a percent)	1.00%
Increase of common shares reserved for future issuance (in shares)				492,722