Reinsurance (Effect on premiums written and earned) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Written:
Treaty reinsurance									$ 1,501,079	$ 1,393,440	$ 1,340,939
Facultative reinsurance									293,741	325,311	334,898
Direct									853,885	838,755	683,028
Ceded	$ (40,635)	$ (45,006)	$ (36,229)	$ (167,835)	$ (33,128)	$ (48,810)	$ (55,418)	$ (191,325)	(289,705)	(328,681)	(313,208)
Net premiums written	298,819	327,412	727,813	1,004,956	276,477	353,699	670,750	927,899	2,359,000	2,228,825	2,045,657
Earned:
Treaty reinsurance									1,408,995	1,397,409	1,338,663
Facultative reinsurance									307,351	330,472	345,252
Direct									823,641	852,256	656,974
Ceded									(290,822)	(333,248)	(347,834)
Net premiums earned	$ 540,399	$ 563,775	$ 573,723	$ 571,268	$ 543,300	$ 555,011	$ 572,688	$ 575,890	2,249,165	2,246,889	1,993,055
Eliminations
Written:
Treaty reinsurance									(26,673)	(42,718)	(53,457)
Facultative reinsurance									0	0	0
Direct									0	0	0
Ceded									26,673	42,718	53,457
Net premiums written									0	0	0
Earned:
Treaty reinsurance									(23,035)	(45,115)	(60,912)
Facultative reinsurance									0	0	0
Direct									0	0	0
Ceded									23,035	45,115	60,912
Net premiums earned									0	0	0
Operating Segments | Validus Re
Written:
Treaty reinsurance									1,111,054	1,126,759	1,118,532
Facultative reinsurance									0	0	0
Direct									0	0	0
Ceded									(111,564)	(149,088)	(163,678)
Net premiums written									999,490	977,671	954,854
Earned:
Treaty reinsurance									1,060,117	1,141,184	1,109,659
Facultative reinsurance									0	0	0
Direct									0	0	0
Ceded									(116,172)	(150,971)	(192,375)
Net premiums earned									943,945	990,213	917,284
Operating Segments | Talbot
Written:
Treaty reinsurance									146,296	133,273	149,079
Facultative reinsurance									293,741	325,311	334,898
Direct									530,665	560,251	617,793
Ceded									(175,729)	(198,896)	(192,211)
Net premiums written									794,973	819,939	909,559
Earned:
Treaty reinsurance									115,828	136,796	163,382
Facultative reinsurance									307,351	330,472	345,252
Direct									529,265	570,669	576,136
Ceded									(170,528)	(199,846)	(204,996)
Net premiums earned									781,916	838,091	879,774
Operating Segments | Western World Insurance Group, Inc
Written:
Treaty reinsurance									0	0	0
Facultative reinsurance									0	0	0
Direct									323,220	278,504	65,235
Ceded									(22,634)	(18,877)	(6,428)	[1]
Net premiums written									300,586	259,627	58,807	[1]
Earned:
Treaty reinsurance									0	0	0
Facultative reinsurance									0	0	0
Direct									294,376	281,587	80,838
Ceded									(21,144)	(22,937)	(7,842)
Net premiums earned									273,232	258,650	72,996	[1]
Operating Segments | AlphaCat & Consolidated Variable Interest Entities
Written:
Treaty reinsurance									270,402	176,126	126,785
Facultative reinsurance									0	0	0
Direct									0	0	0
Ceded									(6,451)	(4,538)	(4,348)
Net premiums written									263,951	171,588	122,437
Earned:
Treaty reinsurance									256,085	164,544	126,534
Facultative reinsurance									0	0	0
Direct									0	0	0
Ceded									(6,013)	(4,609)	(3,533)
Net premiums earned									$ 250,072	$ 159,935	$ 123,001

[1] The results of Western World have been included in the Company’s consolidated results from the October 2, 2014 date of acquisition.