Segments (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Assets	$ 10,714,346	$ 10,344,520
United States Property And Casualty [Member]
Segment Reporting Information [Line Items]
Assets	985,871	914,697
Professional Liability [Member]
Segment Reporting Information [Line Items]
Assets	1,104,892	1,110,592
Accident And Health [Member]
Segment Reporting Information [Line Items]
Assets	242,278	235,950
United States Surety And Credit [Member]
Segment Reporting Information [Line Items]
Assets	189,054	168,389
International [Member]
Segment Reporting Information [Line Items]
Assets	688,828	859,659
Investing [Member]
Segment Reporting Information [Line Items]
Assets	7,228,608	6,800,313
Corporate And Other [Member]
Segment Reporting Information [Line Items]
Assets	$ 274,815	$ 254,920