Reserve for losses and loss expenses (Prior year development) (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2015
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years	[1]	$ (52,885)	$ (93,749)		$ (169,405)	$ (248,026)
Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(33,033)	(50,475)		(89,594)	(106,050)
Talbot
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(18,691)	(35,972)		(69,739)	(123,245)
Western World
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(880)	(5,054)	[1]	(8,464)	(15,639)	[1]
AlphaCat
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(281)	(2,248)		(1,608)	(3,092)
Property
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(22,983)	(40,621)	[1]	(86,323)	(113,318)	[1]
Property | Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(19,736)	(27,613)		(52,036)	(58,437)
Property | Talbot
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(2,429)	(9,706)		(30,969)	(47,141)
Property | Western World
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(553)	(1,054)	[1]	(2,576)	(4,648)	[1]
Property | AlphaCat
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(265)	(2,248)		(742)	(3,092)
Marine
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(13,051)	(28,410)	[1]	(25,478)	(80,403)	[1]
Marine | Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(8,504)	(13,556)		(14,967)	(29,225)
Marine | Talbot
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(4,547)	(14,854)		(10,511)	(51,178)
Specialty
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(16,524)	(20,718)	[1]	(51,716)	(43,314)	[1]
Specialty | Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(4,793)	(9,306)		(22,591)	(18,388)
Specialty | Talbot
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(11,715)	(11,412)		(28,259)	(24,926)
Specialty | AlphaCat
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(16)			(866)	0
Liability
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(327)	(4,000)	[1]	(5,888)	(10,991)	[1]
Liability | Western World
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(327)	$ (4,000)	[1]	(5,888)	$ (10,991)	[1]
Tianjin and 2015 Earthquake | Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		(18,200)
Attritional losses | Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years		$ (14,800)			(160,400)
Event reserves | Validus Re
Increase (decrease) in net reserves for losses and loss expenses in respect of losses occurring in:
Net favorable development on prior years					$ (9,000)

[1] Upon closing the acquisition of Western World, an adjustment of $15,586 was made to increase net reserves to reflect fair value. This adjustment was amortized to income through a reduction in losses and loss expenses of $2,524 and $8,639, respectively, during the three and nine months ended September 30, 2015, benefiting the loss ratio by 3.9 and 4.4 percentage points, respectively. The remaining fair value adjustment of $2,340 was fully amortized during 2015.