Consideration payment due period one.

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Consideration payment due period two.

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Interest income from licencing.

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Significant Accounting Policies.

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No definition available.

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For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Percentage of ownership interest	20.00%		20.00%
Accumulated deficit	$ (68,120)		$ (68,120)			$ (187,756)
License revenue	40,031	$ 6,562	172,422	$ 7,017
Interest income from licensing	6,898		8,253
License [Member]
Significant Accounting Policies [Line Items]
License revenue	40,031	$ 6,555	172,422	$ 7,010
ASU 2014-09 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit					$ (182,953)
ASU 2014-09 [Member] \| AveXis, Inc. [Member]
Significant Accounting Policies [Line Items]
Payments due from related party	30,000		$ 30,000
Consideration payment due period one			2019-01
Consideration payment due period two			2020-01
Interest income from licensing	6,800		$ 8,000
ASU 2014-09 [Member] \| AveXis, Inc. [Member] \| License [Member]
Significant Accounting Policies [Line Items]
License revenue	40,000		172,100
Reduction in Accumulated Deficit [Member] \| ASU 2014-09 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit	3,692		3,692		$ 4,803
Reduction in Accumulated Deficit [Member] \| ASU 2014-09 [Member] \| License [Member]
Significant Accounting Policies [Line Items]
License revenue	(61,244)		(9,529)
Results Without Adoption of Topic 606 \| ASU 2014-09 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit	(71,812)		(71,812)
Results Without Adoption of Topic 606 \| ASU 2014-09 [Member] \| License [Member]
Significant Accounting Policies [Line Items]
License revenue	101,275		181,951
Results Without Adoption of Topic 606 \| ASU 2014-09 [Member] \| AveXis, Inc. [Member]
Significant Accounting Policies [Line Items]
Interest income from licensing	0		0
Results Without Adoption of Topic 606 \| ASU 2014-09 [Member] \| AveXis, Inc. [Member] \| License [Member]
Significant Accounting Policies [Line Items]
License revenue	$ 100,000		$ 180,000