EQUITY AND STOCK-BASED COMPENSATION - Assumptions used to determine fair value of grants awarded (Details) - Restricted stock units
3 Months Ended
Mar. 05, 2020
Mar. 28, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Illiquidity discount   14.60%
Annual Expected Stock Price Volatility 35.80%  
Annual Expected Dividend Yield 0.00%  
Risk-free Interest Rate 1.14%  
Correlations Between Total Shareholder Return for SPX FLOW and Individual Companies in the Composite Group 0.4167  
Composite Group Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Annual Expected Stock Price Volatility 29.90%  
Risk-free Interest Rate 1.14%  
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Correlations Between Total Shareholder Return for SPX FLOW and Individual Companies in the Composite Group 0.1110  
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Correlations Between Total Shareholder Return for SPX FLOW and Individual Companies in the Composite Group 0.7351