Summary of Significant Accounting Policies - Stock-Based Compensation (Details)	Dec. 31, 2016
Stock-Based Compensation
Forfeiture rate (as a percent)	0.00%

The forfeiture rate to date used to calculate stock-based compensation expense.

No definition available.

Name:	avxs_StockIssuedDuringPeriodSharesShareBasedCompensationForfeitedForfeitureRate
Namespace Prefix:	avxs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant