Taxation (Narrative) (Details) - USD ($)		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 22, 2019
Operating Loss Carryforwards [Line Items]
Partial write-down of U.S. deferred tax asset pursuant to the Tax Cuts and Jobs Act of 2017	$ 36,700,000
Increase (decrease) in valuation allowance		$ 40,400,000	$ 5,300,000	$ 11,200,000
Income taxes paid		9,749,000	341,000	$ 343,000
Unrecognized tax benefits		0	0
Interest and penalties accrued on unrecognized tax benefits		$ 0	$ 0
Bermuda
Operating Loss Carryforwards [Line Items]
Statutory income tax rate		0.00%
U.S.
Operating Loss Carryforwards [Line Items]
Expected tax rate		5.00%
Foreign statutory income tax rate		21.00%
Operating loss carryforwards		$ 338,600,000
Ireland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		12.50%
Operating loss carryforwards		$ 5,600,000
U.K.
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		19.00%
Operating loss carryforwards		$ 115,400,000
Singapore
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		17.00%
Operating loss carryforwards		$ 25,400,000
Switzerland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		21.20%
Operating loss carryforwards		$ 186,600,000
Australia
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		30.00%
TMR
Operating Loss Carryforwards [Line Items]
Deferred tax assets, valuation allowance					$ 35,700,000