Expenses incurred on capitalized patents to be abandoned.

No definition available.

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- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

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- Definition

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.

+ References

No definition available.

+ Details

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- 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

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- Definition

Gross carrying amount as of the balance sheet date of certain rights acquired to exercise a certain privilege or pursue a particular business or occupation and which is deemed to have a finite economic life.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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- Definition

The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of a finite-lived intangible asset to fair value.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16373-109275

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Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 31, 2017
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights	$ 216,000	$ 216,000	$ 217,000	$ 216,000	$ 216,000	$ 780,000	$ 29,000	$ 28,000	$ 865,000	$ 1,053,000	$ 29,000
Patents [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights									$ 700,000	600,000	600,000
Initial term of patents									20 years
Patents [Member] \| Research and Development [Member]
Finite Lived Intangible Assets [Line Items]
Book value of patent abandoned									$ 100,000	600,000	300,000
Impairment loss on patent assets									3,800,000
Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights											100,000
EXONDYS 51 [Member]
Finite Lived Intangible Assets [Line Items]
Sales milestone recorded as an in-license right	0				$ 6,600,000				0	$ 6,600,000	$ 1,000,000
EXONDYS 51 [Member] \| Bio Marin [Member]
Finite Lived Intangible Assets [Line Items]
Sales milestone recorded as an in-license right												$ 6,600,000
EXONDYS 51 [Member] \| University of Western Australia [Member]
Finite Lived Intangible Assets [Line Items]
Sales milestone recorded as an in-license right	$ 1,000,000								$ 1,000,000			$ 1,000,000