401(k) Savings plan - Additional Information (Detail) - 401 (k) [Member] - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Jan. 31, 2016	Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]
Contributions to the 401(k) Plan		$ 0.0
Subsequent Event [Member]
Defined Contribution Plan Disclosure [Line Items]
Contributions to the 401(k) Plan	$ 0.6

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.

No definition available.

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Period Type:	duration