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
Reinsurance [Abstract]
Written premiums: Direct									$ 1,569,791	$ 1,227,645	$ 1,268,698
Written premiums: Assumed									4,306,501	4,521,342	3,949,936
Written premiums: Ceded									(498,031)	(492,084)	(213,813)
Net written premiums	$ 1,364,618	$ 1,561,257	$ 1,168,496	$ 1,283,889	$ 1,294,247	$ 1,517,580	$ 1,217,487	$ 1,227,589	5,378,261	5,256,903	5,004,821
Premiums earned: Direct									1,491,163	1,183,498	1,207,833
Premiums earned: Assumed									4,485,021	4,405,253	3,748,824
Premium earned: Ceded									(494,725)	(419,616)	(203,114)
Net premiums earned	$ 1,428,344	$ 1,413,640	$ 1,332,398	$ 1,307,077	$ 1,362,330	$ 1,389,998	$ 1,272,317	$ 1,144,490	5,481,459	5,169,135	4,753,543
Incurred losses and LAE: Direct									1,268,896	1,100,037	1,173,177
Incurred losses and LAE: Assumed									2,152,633	2,160,663	1,833,055
Incurred losses and LAE: Ceded									(319,614)	(354,166)	(205,981)
Net incurred losses and LAE									$ 3,101,915	$ 2,906,534	$ 2,800,251