Ceded Reinsurance (Credit Risk by Reinsurer) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 1,234,504	$ 1,141,110	$ 1,002,919	$ 927,588
Percentage of total	100.00%	100.00%
Ceded Credit Risk, Concentrated Credit Risk [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	685,443	632,233
Percentage of total	55.50%	55.40%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AM Best, A+ Rating [Member] | Munich Re
Ceded Credit Risk [Line Items]
Reinsurance recoverable	214,070	165,036
Percentage of total	17.30%	14.50%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AM Best, A+ Rating [Member] | Axis Capital
Ceded Credit Risk [Line Items]
Reinsurance recoverable	143,063
Percentage of total	11.60%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AM Best, A+ Rating [Member] | Arch Re
Ceded Credit Risk [Line Items]
Reinsurance recoverable	143,037	148,553
Percentage of total	11.60%	13.00%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AM Best, A Rating [Member] | Axis Capital
Ceded Credit Risk [Line Items]
Reinsurance recoverable		137,459
Percentage of total		12.00%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AM Best, A Rating [Member] | Platinum Underwriters
Ceded Credit Risk [Line Items]
Reinsurance recoverable	98,811	104,536
Percentage of total	8.00%	9.20%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AM Best, A Rating [Member] | Markel (including Alterra)
Ceded Credit Risk [Line Items]
Reinsurance recoverable	86,462	76,649
Percentage of total	7.00%	6.70%
Ceded Credit Risk, Not Concentrated Credit Risk [Member]
Ceded Credit Risk [Line Items]
Reinsurance recoverable	$ 549,061	$ 508,877
Percentage of total	44.50%	44.60%