COMMITMENTS AND CONTINGENT LIABILITIES (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) drilling_unit	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Rental expense	$ 7.4	$ 11.4	$ 10.6
Future minimum payments to be made under noncancelable operating leases [Abstract]
2019	7.6
2020	5.1
2021	1.9
2022	1.8
2023	1.8
Later years	10.0
Total	28.2
Purchase obligations	128.0
Debt Instrument [Line Items]
Letters of credit outstanding	9.1
IRS proposed unfavorable tax adjustments	85.0
Gross unrecognized tax benefits	98.2	$ 102.0	$ 120.1	$ 65.1
Tax impact of unrecognized tax benefits, if reversed	35.0
New Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Letters of credit outstanding	$ 6.8
Saudi Arabia Joint Venture [Member]
Debt Instrument [Line Items]
Period Of Joint Venture Funding Of Drilling Rigs	10 years
Saudi Arabia Joint Venture [Member] | Maximum [Member]
Debt Instrument [Line Items]
Number Of Drilling Rigs To Be Purchased By Joint Venture | drilling_unit	20
Contingent Funding Obligation To Equity Method Investment	$ 1,250.0
Number Of Drilling Rigs To Be Purchased By Each Partner in a 12 month period | drilling_unit	3