Segments (Assets by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Assets	$ 11,140,930	$ 10,714,346
North America Property & Casualty [Member]
Segment Reporting Information [Line Items]
Assets	2,465,227	1,894,756
Accident & Health [Member]
Segment Reporting Information [Line Items]
Assets	243,105	242,278
International [Member]
Segment Reporting Information [Line Items]
Assets	1,131,605	1,073,889
Investing [Member]
Segment Reporting Information [Line Items]
Assets	7,052,910	7,228,608
Corporate & Other [Member]
Segment Reporting Information [Line Items]
Assets	$ 248,083	$ 274,815