Stockholder Rights Plan (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
Mar. 27, 2018	Dec. 31, 2018
Equity [Abstract]
Redemption price per share (in USD per share)	$ 0.01
Redemption of stockholders' rights agreement	$ 400	$ 411

Redemption Price Per Share Of Stockholders' Rights Agreement

No definition available.

Name:	bdc_RedemptionPricePerShareOfStockholdersRightsAgreement
Namespace Prefix:	bdc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant