Subsequent Event (detail) $ in Millions	Jan. 19, 2017 USD ($)
Subsequent Events [Abstract]
Property Insurance Deductable	$ 5

The amount of Property Insurance that is subject to a deductable

No definition available.

Name:	senea_Propertyinsurancedeductable
Namespace Prefix:	senea_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant