STOCKHOLDERS' EQUITY - AOCI Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amortization of pension and other post-retirement liability adjustments
Tax (benefit) expense									$ 24,896	$ (1,600)	$ 45,424
Net earnings	$ 24,542	$ 20,323	$ 13,123	$ 15,267	$ 32,679	$ 19,161	$ 12,960	$ 15,396	73,255	80,192	82,114
Amounts reclassified from accumulated other comprehensive income (loss)
Amortization of pension and other post-retirement liability adjustments
Prior service credits									730	1,485	1,120
Actuarial losses									(917)	(707)	(244)
Loss recognized during settlement									(5,735)	(2,162)	0
Total before tax									(5,922)	(1,384)	876
Tax (benefit) expense									(1,502)	(548)	312
Net earnings									$ (4,420)	$ (836)	$ 564