Income Taxation - Net Operating Loss Carryforwards (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Tax effect of operating loss carryforward	$ 159,436	$ 183,633
Foreign Tax Authority | United States
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	513,476
Tax effect of operating loss carryforward	107,830
Foreign Tax Authority | United Kingdom
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	224,150
Tax effect of operating loss carryforward	38,106
Foreign Tax Authority | Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	52,484
Tax effect of operating loss carryforward	$ 13,500