RESTRUCTURING ACTIVITIES AND SPIN-OFF TRANSACTION COSTS - Additional Information (Details) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) employee	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Employee Severance
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | employee	74
Restructuring, expected annual savings	$ 18.3	$ 18.3		$ 18.3
Restructuring, expected cost	5.5	5.5		5.5
Restructuring, incurred costs	3.4
Expected savings due to benefit changes and other initiatives	$ 15.8	15.8		$ 15.8
Positions eliminated, percent of total				9.00%
Employee Severance | Babcock & Wilcox Volund Workforce
Restructuring Cost and Reserve [Line Items]
Positions eliminated, percent of total				30.00%
Employee Severance | Executive
Restructuring Cost and Reserve [Line Items]
Restructuring, incurred costs		$ 0.2		$ 5.1
Spinoff | Selling, General and Administrative Expenses
Restructuring Cost and Reserve [Line Items]
Spin-off costs			$ 0.5	$ 0.3	$ 0.9