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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 |  |

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- Definition Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6409961&loc=d3e20487-108367 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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