Revenue (Narrative) (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Transferred Over Time [Member]
Disaggregation Of Revenue [Line Items]
Percentage Of Revenue	93.00%	93.40%	92.70%

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