Income Taxes - Effective Tax Reconciliation (Details) - UK income tax	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Tax rates which are different than the UK and Cayman Island rates	4.30%	5.00%	23.40%
Tax impact of asset impairment and disposition	0.30%	2.90%	11.70%
Tax impact of tax restructuring	(4.10%)	0.00%	(76.10%)
Tax impact of the Tax Cuts and Jobs Act	0.00%	2.10%	33.40%
Tax impact of valuation allowance	0.50%	(1.00%)	0.00%
Resolution of (reserve for) tax authority audits	3.20%	(0.40%)	(1.90%)
Total	4.20%	8.60%	(9.50%)