Schedule III - Supplementary insurance information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	$ 209,227	$ 181,002	$ 161,022
Reserve for losses and loss expenses	2,995,195	2,996,567	3,243,147
Unearned premiums	1,076,049	966,210	989,229
Net premiums earned	2,249,165	2,246,889	1,993,055
Net investment income	150,385	127,824	100,086
Losses and loss expenses	1,065,097	977,833	765,015
Amortization of deferred acquisition costs	449,482	410,058	339,467
Other operating expenses	379,201	402,050	362,435
Net premiums written	2,359,000	2,228,825	2,045,657
Validus Re
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	79,588	60,459	59,091
Reserve for losses and loss expenses	1,116,753	1,146,869	1,333,878
Unearned premiums	352,646	294,509	305,138
Net premiums earned	943,945	990,213	917,284
Net investment income	0	0	0
Losses and loss expenses	411,488	457,976	307,290
Amortization of deferred acquisition costs	181,040	166,387	141,670
Other operating expenses	83,804	88,778	84,478
Net premiums written	999,490	977,671	954,854
Talbot
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	95,237	92,095	95,246
Reserve for losses and loss expenses	1,301,517	1,302,635	1,352,056
Unearned premiums	551,815	533,558	552,660
Net premiums earned	781,916	838,091	879,774
Net investment income	0	0	0
Losses and loss expenses	424,946	347,322	423,394
Amortization of deferred acquisition costs	177,127	187,535	187,162
Other operating expenses	147,557	167,679	162,174
Net premiums written	794,973	819,939	909,559
Western World Insurance Group, Inc
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	34,841	28,622	9,566
Reserve for losses and loss expenses	589,500	600,331	613,551
Unearned premiums	158,945	130,101	133,185
Net premiums earned	273,232	258,650	72,996
Net investment income	0	0	0
Losses and loss expenses	183,812	171,878	51,035
Amortization of deferred acquisition costs	64,442	41,408	3,169
Other operating expenses	45,823	40,798	11,256
Net premiums written	300,586	259,627	58,807
AlphaCat
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	4,060	2,526	1,281
Reserve for losses and loss expenses	48,534	11,013	15,278
Unearned premiums	38,961	24,643	13,060
Net premiums earned	250,072	159,935	123,001
Net investment income	0	0	0
Losses and loss expenses	44,851	657	(16,704)
Amortization of deferred acquisition costs	26,905	16,327	11,584
Other operating expenses	34,582	39,635	36,799
Net premiums written	263,951	171,588	122,437
Corporate & Eliminations
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	(4,499)	(2,700)	(4,162)
Reserve for losses and loss expenses	(61,109)	(64,281)	(71,616)
Unearned premiums	(26,318)	(16,601)	(14,814)
Net premiums earned	0	0	0
Net investment income	150,385	127,824	100,086
Losses and loss expenses	0	0	0
Amortization of deferred acquisition costs	(32)	(1,599)	(4,118)
Other operating expenses	67,435	65,160	67,728
Net premiums written	$ 0	$ 0	$ 0