Commitments and Contingencies - Self Insurance Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Self-Insurance disclosures
Employer's liability claims subject to per-occurrence deductible	$ 3,000
Workers automobile claims	2,500
General liability claims subject to per-occurrence deductible	5,000
Deductions in land rigs and for offshore rigs	5,000
Self-insurance accruals	150,900	$ 157,400
Self-insurance recoveries/receivables	29,000
South America Africa the Middle East and Asia Excluding Colombia
Self-Insurance disclosures
Political risk insurance losses deductible	250
COLOMBIA
Self-Insurance disclosures
Political risk insurance deductible for foreign operation	500
Latin American tax authority | Minimum
Income tax
Aggregate remaining amounts assessed or expected to assessed range	3,000
Latin American tax authority | Maximum
Income tax
Aggregate remaining amounts assessed or expected to assessed range	$ 8,000