Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) (Unaudited)	3 Months Ended
Mar. 31, 2013
Statement of Stockholders' Equity [Abstract]
Constructively retired treasury shares	382,380

Number of shares of common stock in treasury accounted for as constructively retired and not included in the number of shares outstanding.

No definition available.

Name:	blt_ConstructivelyRetiredTreasuryShares
Namespace Prefix:	blt_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration