LEASES (Components of Nonmineral Lease Expense) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
LEASES [Abstract]
Operating lease cost		$ 14,167		$ 28,294
Short-term lease cost	[1]	7,922		16,623
Variable lease cost		3,489		6,557
Sublease income		(807)		(1,418)
Total lease cost		$ 24,771	$ 21,968	$ 50,056	$ 46,320

[1] We have elected to recognize the cost of leases with an initial term of one month or less within our short-term lease cost.