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EMPLOYEE BENEFIT PLANS (Detail) - USD ($)
shares in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Employee Stock Purchase Plan [Line Items]      
Employer contributions vesting period 2 years    
Employer contributions $ 2,357,000 $ 1,608,000 $ 1,319,000
Multiemployer pension plan withdrawal obligation 1,757,000 3,194,000  
Withdrawal costs - multiemployer pension plan 0 3,591,000 0
Reversal of pension costs   $ 397,000  
Contingent liability term   17 years  
Multiemployer pension plan withdrawal obligation, undiscounted   $ 4,224,000  
Estimated accumulated benefit obligation as complete withdrawal   18,511,000  
New England Teamsters and Trucking Industry Pension Fund | Multiemployer Pension Plans      
Employee Stock Purchase Plan [Line Items]      
Multiemployer plan, employer contribution, cost $ 390,000 $ 409,000 $ 726,000
Hourly employees | First matching contribution      
Employee Stock Purchase Plan [Line Items]      
Employer matching contribution, percent of match 100.00%    
Employer matching contribution, percent of employees' annual income 1.00%    
Hourly employees | Next matching contribution      
Employee Stock Purchase Plan [Line Items]      
Employer matching contribution, percent of match 50.00%    
Employer matching contribution, percent of employees' annual income 3.00%    
Salary employees      
Employee Stock Purchase Plan [Line Items]      
Employer matching contribution, percent of match 50.00%    
Maximum annual contributions per employee $ 1,500    
Class A Common Stock      
Employee Stock Purchase Plan [Line Items]      
Discount rate 15.00%    
Stock issued under stock purchase plan (in shares) 20 23 26
Stock available for distribution under stock purchase plan (in shares) 74