ACCRUED EXPENSES (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
ACCRUED EXPENSES.
Workers' compensation, third-party casualty, and loss and damage claims reserves	$ 116,535	$ 103,898
Accrued vacation pay	52,746	51,728
Accrued compensation, including retirement benefits	110,755	67,690
Taxes other than income	10,225	10,468
Other	15,590	12,962
Total accrued expenses	$ 305,851	$ 246,746