LEASES - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of Use Asset - Operating Leases	$ 87,026
Present value of minimum lease payments	90,200
Gross property, plant and equipment	4,878,730		$ 4,838,171
Accumulated depreciation	2,778,448		$ 2,731,643
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of Use Asset - Operating Leases		$ 92,000
Present value of minimum lease payments		$ 92,000
Operating lease
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross property, plant and equipment	10,097
Accumulated depreciation	$ 10,097