Reserve for losses and loss expenses (Reconciliation of loss development information to reserves for losses and loss expenses) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	$ 2,459,039
Loss reserves recoverable	430,421	$ 350,586	$ 377,466	$ 370,154
Unallocated loss adjustment expenses	51,990
Allowance for reinsurance recoverable	5,153	4,997
Other	58
Reserve for losses and loss expenses	2,995,195	$ 2,996,567	$ 3,243,147	$ 3,047,933
Validus Re | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	419,487
Loss reserves recoverable	42,873
Validus Re | Marine
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	301,516
Loss reserves recoverable	52,970
Validus Re | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	291,372
Loss reserves recoverable	2,162
Talbot | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	233,147
Loss reserves recoverable	93,774
Talbot | Marine
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	397,145
Loss reserves recoverable	125,677
Talbot | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	342,359
Loss reserves recoverable	86,587
Western World Insurance Group, Inc | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	18,766
Loss reserves recoverable	187
Western World Insurance Group, Inc | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserves for losses and loss expenses, net of reinsurance	455,247
Loss reserves recoverable	87,300
AlphaCat
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Reserve for losses and loss expenses	48,534
Corporate & Eliminations
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss reserves recoverable	$ (61,109)