Segment information (Segment reporting by segment - Underwriting activities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Gross premiums written	$ 1,832,456	$ 1,190,857
Reinsurance premiums ceded	(376,294)	(200,106)
Net premiums written	1,456,162	990,751
Change in unearned premiums	(837,220)	(415,375)
Net premiums earned	618,942	575,376
Other insurance related income (loss)	25,496	1,236
Segmental revenues	644,438	576,612
Losses and loss expenses	321,545	269,585
Policy acquisition costs	116,456	111,628
General and administrative expenses	114,726	87,924
Share compensation expenses	9,729	9,491
Total underwriting deductions	562,456	478,628
Segmental (loss) income	81,982	97,984
Net (loss) income (attributable) available to Validus common shareholders	(4,078)	94,561
Operating Segments | Reinsurance segment
Segment Reporting Information [Line Items]
Gross premiums written	765,573	643,141
Reinsurance premiums ceded	(190,194)	(114,446)
Net premiums written	575,379	528,695
Change in unearned premiums	(350,627)	(297,040)
Net premiums earned	224,752	231,655
Other insurance related income (loss)	2	2
Segmental revenues	224,754	231,657
Losses and loss expenses	103,473	80,881
Policy acquisition costs	48,340	43,535
General and administrative expenses	28,915	19,969
Share compensation expenses	2,663	2,623
Total underwriting deductions	183,391	147,008
Segmental (loss) income	41,363	84,649
Net (loss) income (attributable) available to Validus common shareholders	$ 41,363	$ 84,649
Net premiums written / Gross premiums written	75.20%	82.20%
Loss and loss expense ratio	46.00%	34.90%
Policy acquisition cost ratio	21.50%	18.80%
General and administrative expenses	14.10%	9.80%
Expense ratio	35.60%	28.60%
Combined ratio	81.60%	63.50%
Operating Segments | Insurance segment
Segment Reporting Information [Line Items]
Gross premiums written	$ 785,795	$ 382,790
Reinsurance premiums ceded	(191,637)	(79,000)
Net premiums written	594,158	303,790
Change in unearned premiums	(294,620)	(24,696)
Net premiums earned	299,538	279,094
Other insurance related income (loss)	2,170	996
Segmental revenues	301,708	280,090
Losses and loss expenses	183,389	186,610
Policy acquisition costs	60,057	61,192
General and administrative expenses	68,050	45,276
Share compensation expenses	2,989	3,373
Total underwriting deductions	314,485	296,451
Segmental (loss) income	(12,777)	(16,361)
Net (loss) income (attributable) available to Validus common shareholders	$ (12,777)	$ (16,361)
Net premiums written / Gross premiums written	75.60%	79.40%
Loss and loss expense ratio	61.20%	66.90%
Policy acquisition cost ratio	20.00%	21.90%
General and administrative expenses	23.70%	17.40%
Expense ratio	43.70%	39.30%
Combined ratio	104.90%	106.20%