Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Fair Value of Financial Instruments [Line Items]
Restricted cash	$ 527,000	$ 4,409,000
Note payable, percentage of interest rate change	1.00%
Fair value of note payable to related party, description	The fair value measurement of the note payable is sensitive to the change in interest rate. If the interest rate changes by approximately 1%, the fair value of the note payable would change by $1 million or 1.4%.
Change in fair value of note payable value due to change in interest rate percentage	$ 1,000,000
Change in fair value of note payable percentage due to change in interest rate percentage	1.40%
Fair value of the liability, percentage decrease	8.00%
Minimum
Fair Value of Financial Instruments [Line Items]
Probabilities of meeting the milestones, amount	$ 50,000,000
Probabilities of meeting the milestones, percentage decrease	5.00%
Fair value of the liability, percentage decrease	13.00%
Maximum
Fair Value of Financial Instruments [Line Items]
Probabilities of meeting the milestones, amount	$ 200,000,000
Probabilities of meeting the milestones, percentage decrease	10.00%
Fair value of the liability, percentage decrease	25.00%
Money Market Funds
Fair Value of Financial Instruments [Line Items]
Cash equivalents	$ 23,400,000	41,000,000
Restricted cash	$ 500,000	$ 4,400,000

Change in fair value of note payable percentage due to change in interest rate percentage.

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- Definition

Change in fair value of note payable value due to change in interest rate percentage.

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Fair value of financial instruments.

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Fair value of liability, percentage decrease.

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Fair value of liability percentage decrease if probabilities of meeting milestones percentage decrease.

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- Definition

Fair value of note payable to related party description.

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Note payable, percentage of interest rate change.

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Probabilities of meeting milestones amount.

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Probabilities of meeting milestones, percentage decrease.

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- Definition

Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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Amount of cash restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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-Name Accounting Standards Codification
-Topic 210
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