Balance Sheet Components - Build-to-Suit Lease Asset, Net (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Build To Suit Lease Assets [Abstract]
Build-to-suit lease asset	$ 8,986
Less: Accumulated depreciation and amortization	(98)
Build-to-suit lease asset, net	$ 8,888

Build to suit lease asset noncurrent accumulated depreciation and amortization.

No definition available.

Name:	vsar_BuildToSuitLeaseAssetNoncurrentAccumulatedDepreciationAndAmortization
Namespace Prefix:	vsar_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant