Reinsurance (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
Premiums Written, Net [Abstract]
Gross premiums written									$ 5,547,525	$ 5,932,003	$ 5,569,706
Ceded									317,977	212,119	173,180
Net	$ 1,064,000	$ 1,190,000	$ 1,322,000	$ 1,653,000	$ 1,220,000	$ 1,343,000	$ 1,419,000	$ 1,738,000	5,229,548	5,719,884	5,396,526
Premiums earned
Assumed									5,570,321	5,824,398	5,373,866
Ceded									301,143	215,203	175,656
Net	1,294,000	1,412,000	1,328,000	1,235,000	1,446,000	1,557,000	1,353,000	1,254,000	5,269,178	5,609,195	5,198,210
Loss and Loss Expenses and Life Policy Benefits
Assumed									3,215,665	3,503,060	3,207,860
Ceded									58,245	40,290	50,052
Net	767,000	$ 804,000	$ 865,000	$ 721,000	870,000	$ 960,000	$ 884,000	$ 749,000	3,157,420	3,462,770	$ 3,157,808
Allowance For Reinsurance Recoverable [Member]
Allowance for uncollectible reinsurance recoverable [Line Items]
Allowance for uncollectible reinsurance recoverable	$ 9,000				$ 13,000				$ 9,000	$ 13,000