OPERATING LEASES (Tables)

12 Months Ended

Dec. 31, 2017

OPERATING LEASES [Abstract]

Rental Expense from Continuing Operations under Nonmineral Operating Leases

in thousands	2017	2016	2015
Operating Leases
Minimum rentals	$        59,536	$       52,713	$       49,461
Contingent rentals (based principally on usage)	50,822	57,278	60,380
Total	$      110,358	$     109,991	$     109,841

Future Minimum Operating Lease Payments

in thousands
Future Minimum Operating Lease Payments
2018	$        36,358
2019	33,986
2020	30,888
2021	27,331
2022	20,880
Thereafter	106,351
Total	$      255,794