Taxation (Details) - Narrative (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Line Items]
Deferred tax asset, per balance sheet	$ 166,142,000	$ 115,601,000
Deferred tax liability, per balance sheet	141,803,000	91,104,000
Valuation allowance	297,637,000	497,236,000
United States
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	35.00%
United States | Capital loss carryforward
Income Tax Disclosure [Line Items]
Capital loss valuation allowance, amount	99,000,000
Capital loss carryforwards, tax effected	99,000,000
Capital loss carryforwards available	282,800,000
Limitation on use, in years	5 years
United States | Deferred intercompany capital losses
Income Tax Disclosure [Line Items]
Capital loss valuation allowance, amount	97,600,000
Capital loss carryforwards, tax effected	97,600,000
Capital loss carryforwards available	278,800,000
United States | Not expected to be utilized in the future
Income Tax Disclosure [Line Items]
Capital loss valuation allowance, amount	196,500,000	237,200,000
United States | Expiring in 2013
Income Tax Disclosure [Line Items]
Capital loss carryforwards available	54,100,000
United States | Expiring in future years
Income Tax Disclosure [Line Items]
Capital loss carryforwards available	228,700,000
Ireland
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	150,900,000
Ireland | Active income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	12.50%
Ireland | Passive income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	25.00%
Ireland | Capital loss carryforward
Income Tax Disclosure [Line Items]
Capital loss carryforwards available	122,100,000
Ireland | Net operating loss and capital loss carryforward
Income Tax Disclosure [Line Items]
Capital loss valuation allowance, amount	59,200,000	53,100,000
Bermuda
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	0.00%
United Kingdom
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	24.50%
Net operating loss carryforwards, amount	45,200,000
Net operating loss carryforwards, tax effected	10,500,000
Potential valuation allowance on net operating losses	8,700,000
United Kingdom | Not expected to be utilized in the future
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	7,800,000
Net operating loss carryforwards valuation allowance, amount	1,800,000
United Kingdom | Expected to be used
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	37,400,000
Switzerland
Income Tax Disclosure [Line Items]
Capital loss valuation allowance, amount	166,400,000
Net operating loss carryforwards, amount	68,300,000	183,100,000
Net operating loss carryforwards valuation allowance, amount	9,900,000
Net operating loss carryforwards that expired during the period, amount	784,800,000
Switzerland | Active income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	7.83%
Switzerland | Passive income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	21.20%
Switzerland | Expiring in 2013
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	7,100,000
Switzerland | Expiring in future years
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	$ 62,800,000
Germany
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	15.00%
France
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	36.13%