Funds Held - Directly Managed Funds Held - Directly Managed Investment Income - (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Investment Income [Line Items]
Net investment income	$ 115,000	$ 118,000	$ 130,000	$ 117,000	$ 114,000	$ 122,000	$ 125,000	$ 124,000	$ 479,696	$ 484,367	$ 571,338
Funds held directly managed [Member]
Net Investment Income [Line Items]
Net investment income									13,841	20,502	29,031
Funds held directly managed [Member] | Fixed maturities
Net Investment Income [Line Items]
Net investment income									12,789	18,804	27,760
Funds held directly managed [Member] | Short Term Investments, Cash And Cash Equivalents[Member]
Net Investment Income [Line Items]
Net investment income									59	1,246	1,046
Funds held directly managed [Member] | Other [Member]
Net Investment Income [Line Items]
Net investment income									1,760	1,287	1,647
Funds held directly managed [Member] | Investment Expenses [Member]
Net Investment Income [Line Items]
Net investment income									$ (767)	$ (835)	$ (1,422)