Condensed unaudited quarterly financial information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Gross premiums written	$ 443,323	$ 523,856	$ 792,902	$ 1,190,857	$ 339,454	$ 372,418	$ 764,042	$ 1,172,791	$ 2,950,938	$ 2,648,705	$ 2,557,506
Reinsurance premiums ceded	(96,445)	(116,860)	(56,222)	(200,106)	(40,635)	(45,006)	(36,229)	(167,835)	(469,633)	(289,705)	(328,681)
Net premiums written	346,878	406,996	736,680	990,751	298,819	327,412	727,813	1,004,956	2,481,305	2,359,000	2,228,825
Change in unearned premiums	304,599	316,212	(105,653)	(415,375)	241,580	236,363	(154,090)	(433,688)	99,783	(109,835)	18,064
Net premiums earned	651,477	723,208	631,027	575,376	540,399	563,775	573,723	571,268	2,581,088	2,249,165	2,246,889
Net investment income	48,960	44,458	44,241	40,214	38,153	43,514	39,257	29,461	177,873	150,385	127,824
Net realized gains on investments	5,607	906	2,274	(1,164)	9,220	4,397	2,724	(584)	7,623	15,757	2,298
Change in net unrealized gains (losses) on managed investments	(21,257)	(5,197)	16,321	13,348	(67,460)	5,459	31,428	47,444	3,215	16,871	(32,395)
Income (loss) from investment affiliates	6,345	1,011	9,466	5,188	2,166	453	(589)	(4,113)	22,010	(2,083)	4,281
Other insurance related income and other income	6,939	3,571	1,339	1,330	568	(610)	824	1,413	13,179	2,195	5,111
Foreign exchange (losses) gains	(283)	(1,404)	(7,329)	1,569	(901)	(766)	6,286	6,245	(7,447)	10,864	(8,731)
Total Revenues	697,788	766,553	697,339	635,861	522,145	616,222	653,653	651,134	2,797,541	2,443,154	2,345,277
Expenses
Losses and loss expenses	479,842	1,254,602	296,149	269,585	275,126	258,394	307,130	224,447	2,300,178	1,065,097	977,833
Policy acquisition costs	127,067	115,590	117,268	111,628	120,889	113,434	107,966	107,193	471,553	449,482	410,058
General and administrative expenses	97,522	70,342	96,349	87,924	77,955	82,443	89,688	86,208	352,137	336,294	363,709
Share compensation expenses	10,031	9,443	11,146	9,491	10,442	10,501	10,727	11,237	40,111	42,907	38,341
Finance expenses	15,871	14,523	14,209	13,943	14,630	14,521	14,166	15,203	58,546	58,520	74,742
Transaction expenses	0	0	4,427	0					4,427	0	0
Total expenses	730,333	1,464,500	539,548	492,571	499,042	479,293	529,677	444,288	3,226,952	1,952,300	1,864,683
Income before taxes, loss from operating affiliate and (income) attributable to AlphaCat investors	(32,545)	(697,947)	157,791	143,290	23,103	136,929	123,976	206,846	(429,411)	490,854	480,594
Tax benefit (expense)	412	2,632	987	3,549	21,147	(1,830)	(1,706)	2,118	7,580	19,729	(6,376)
(Loss) income from operating affiliates					0	0	0	(23)	0	(23)	(3,949)
Loss (income) attributable to AlphaCat investors	(37,868)	74,130	(11,830)	(7,503)	(7,080)	(5,564)	(6,114)	(4,600)	16,929	(23,358)	(2,412)
Net income (loss)	(70,001)	(621,185)	146,948	139,336	37,170	129,535	116,156	204,341	(404,902)	487,202	467,857
Net loss (income) attributable to noncontrolling interests	67,136	376,366	(43,650)	(42,572)	(27,200)	(37,439)	(21,193)	(37,531)	357,280	(123,363)	(92,964)
Net income available to Validus	(2,865)	(244,819)	103,298	96,764	9,970	92,096	94,963	166,810	(47,622)	363,839	374,893
Dividends on preferred shares	(5,828)	(5,627)	(2,203)	(2,203)	(2,203)	(2,252)	0	0	(15,861)	(4,455)	0
Net income available to Validus common shareholders	$ (8,693)	$ (250,446)	$ 101,095	$ 94,561	$ 7,767	$ 89,844	$ 94,963	$ 166,810	$ (63,483)	$ 359,384	$ 374,893
Earnings per share
Basic (loss) earnings per share (attributable) available to Validus common shareholders	$ (0.11)	$ (3.17)	$ 1.28	$ 1.19	$ 0.10	$ 1.12	$ 1.16	$ 2.01	$ (0.80)	$ 4.43	$ 4.47
(Loss) earnings per diluted share (attributable) available to Validus common shareholders	(0.11)	(3.17)	1.25	1.17	0.10	1.11	1.14	1.98	(0.80)	4.36	4.34
Cash dividends declared per share	$ 0.38	$ 0.38	$ 0.38	$ 0.38	$ 0.35	$ 0.35	$ 0.35	$ 0.35	$ 1.52	$ 1.40	$ 1.28