Revenue (Narrative) (Details)	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Transferred Over Time [Member]
Disaggregation Of Revenue [Line Items]
Percentage Of Revenue	95.30%	95.60%

Percentage, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

No definition available.

Name:	bhe_PercentageOfRevenue
Namespace Prefix:	bhe_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration