REVENUE RECOGNITION AND CONTRACTS - SPIG's Loss Contract (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Dec. 31, 2017 contract
Disaggregation of Revenue [Line Items]
Number of contracts in a loss position | contract					6
Renewable loss contracts, net gain (loss) recognized on changes in estimated revenues and costs	$ (1,100,000)	$ (700,000)	$ (1,400,000)	$ (8,000,000)
B&W Thermal segment
Disaggregation of Revenue [Line Items]
Number of contracts in a loss position | contract	2		2
Renewable loss contracts, net gain (loss) recognized on changes in estimated revenues and costs	$ (1,300,000)	$ 0	$ (1,300,000)
B&W Thermal segment | Second SPIG Contract
Disaggregation of Revenue [Line Items]
Renewable loss contracts, net gain (loss) recognized on changes in estimated revenues and costs				$ 700,000
Percent complete	97.00%	98.00%	97.00%	98.00%
Reserve for estimated contract losses	$ 200,000		$ 200,000
Contract, accrued losses		$ 100,000		$ 100,000
Additional contract charges			$ 3,300,000
B&W Thermal segment | First SPIG Contract
Disaggregation of Revenue [Line Items]
Percent complete	100.00%	97.00%	100.00%	97.00%
Reserve for estimated contract losses	$ 0		$ 0
Contract, accrued losses		$ 500,000		$ 500,000