Taxation (Narrative) (Details) - USD ($)		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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		$ 5,300,000	$ (11,200,000)	$ (900,000)
Valuation allowance		35,271,000	30,016,000
Income taxes paid (refunded)		341,000	343,000	$ (1,118,000)
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%
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Expected tax rate		5.00%
Foreign statutory income tax rate		21.00%
Operating loss carryforwards		$ 164,200,000
Ireland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		12.50%
Operating loss carryforwards		$ 4,800,000
U.K.
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		19.00%
Increase (decrease) in valuation allowance		$ 4,000,000
Operating loss carryforwards		$ 114,400,000
Singapore
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		17.00%
Operating loss carryforwards		$ 21,700,000
Switzerland
Operating Loss Carryforwards [Line Items]
Foreign statutory income tax rate		21.20%