PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS (Nonunion) (Details) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($) plan person	Mar. 31, 2019	Sep. 30, 2018 USD ($)	Sep. 30, 2019	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Pension and other postretirement benefit plans
Pension settlement expense					$ 8,135	$ 1,603
Pension settlement expense, net of tax	$ 5,850		$ 384		7,063	1,190
Noncash charge to pension settlement expense	$ 4,000				4,000
Nonunion Defined Benefit Pension Plan
Pension and other postretirement benefit plans
Number of plan participants for which vested pension benefits were settled | person	120
Number of plan participants for which benefit obligation was transferred to PBGC. | plan	30
Pension settlement expense	$ 2,530		518		4,164	1,603
Pension settlement expense, net of tax	1,900		400		3,100	1,200
Lump-sum distributions	16,000		$ 3,100		33,900	$ 11,600
Nonparticipating annuity contract purchase price	14,000
Payment to purchase annuity contract	14,000
Transfer of remaining obligation to PGBC	1,500
Noncash charge to pension settlement expense	4,000				4,000
Employer contributions	$ 7,700				$ 7,710
Expected return on plan assets (as a percent)		1.40%		0.00%