Goodwill and Intangible Assets Allocation to Segments - (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Goodwill Allocation to Segments [Line Items]
Goodwill	$ 456,380	$ 456,380
Life and Health [Member]
Goodwill Allocation to Segments [Line Items]
Goodwill	18,804	18,804
North America Segment [Member] | Non Life [Member]
Goodwill Allocation to Segments [Line Items]
Goodwill	82,026	82,026
Global (Non-US) P&C [Member] | Non Life [Member]
Goodwill Allocation to Segments [Line Items]
Goodwill	149,895	149,895
Global Specialty [Member] | Non Life [Member]
Goodwill Allocation to Segments [Line Items]
Goodwill	179,641	179,641
Catastrophe Segment [Member] | Non Life [Member]
Goodwill Allocation to Segments [Line Items]
Goodwill	$ 26,014	$ 26,014