INCOME TAXES - Rate Reconciliation (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended								10 Months Ended	12 Months Ended
	Feb. 28, 2018	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation between the effective income tax rate, as computed on income (loss) before income taxes, and the statutory federal income tax rate
Income tax provision at the statutory federal rate											$ 19,424	$ 10,809	$ 17,721
Federal income tax effects of:
State income taxes											(1,062)	(637)	(840)
Nondeductible expenses											1,395	1,344	1,682
Life insurance proceeds and changes in cash surrender value											(488)	(775)	7
Alternative fuel tax credit											(1,261)	(2,340)	(1,203)
Net increase (decrease) in valuation allowances											617	382	(891)
Net increase (decrease) in uncertain tax positions											(933)	(20)	933
Settlement of share-based compensation											420	388	(649)
Impact of the Tax Reform Act on current tax													(52)
Impact of the Tax Reform Act on deferred tax													(3,772)
Nonunion pension termination expense												1,040
Foreign tax credits generated											(391)	(2,054)	(2,216)
Federal research and development tax credits											(2,078)	(1,354)
Other											306	(385)	187
Federal income tax provision											15,949	6,398	10,907
State income tax provision											5,056	3,034	4,001
Foreign income tax provision											391	2,054	2,216
Total provision (benefit) for income taxes		$ 6,285	$ 9,774	$ 4,854	$ 483	$ (6,478)	$ 7,072	$ 9,184	$ 1,708		$ 21,396	$ 11,486	$ 17,124
Effective tax (benefit) rate (as a percent)											23.10%	22.30%	20.30%
Statutory federal rate (as a percent)	32.74%									21.00%	21.00%	21.00%	21.00%	35.00%
Income taxes paid, excluding income tax refunds											$ 28,600	$ 28,100	$ 21,800
Income tax refunds											$ 13,300	$ 13,100	$ 18,500