Funds Held - Directly Managed Funds Held - Directly Managed Investment Income - (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income [Line Items]
Net investment income	$ 108,000	$ 117,000	$ 120,000	$ 105,000	$ 115,000	$ 118,000	$ 130,000	$ 117,000	$ 449,784	$ 479,696	$ 484,367
Funds held directly managed [Member]
Net Investment Income [Line Items]
Net investment income									11,676	13,841	20,502
Funds held directly managed [Member] | Fixed maturities
Net Investment Income [Line Items]
Net investment income									10,528	12,789	18,804
Funds held directly managed [Member] | Short Term Investments, Cash And Cash Equivalents[Member]
Net Investment Income [Line Items]
Net investment income									81	59	1,246
Funds held directly managed [Member] | Other [Member]
Net Investment Income [Line Items]
Net investment income									1,776	1,760	1,287
Funds held directly managed [Member] | Investment Expenses [Member]
Net Investment Income [Line Items]
Net investment income									$ (709)	$ (767)	$ (835)