Related party transactions (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Aquiline Capital Partners LLC
Related Party Transaction [Line Items]
Shares owned by related party	3,446,643
Warrants to purchase shares	2,756,088
Related Parties Number Of Employees	2
Group Ark Insurance Holdings Ltd
Related Party Transaction [Line Items]
Gross premiums written	$ 1,373	$ 1,795
Premiums receivable	181		242
Reinsurance premiums ceded	5	4
Loss reserves recoverable	2,688		3,698
Earned premium adjustments	1,441	719
Conning Inc
Related Party Transaction [Line Items]
Investment management fees	56	191
Accounts payable and accrued expenses	170		283
Aquiline Capital Partners II GP Offshore Ltd
Related Party Transaction [Line Items]
Accounts payable and accrued expenses	0
Percentage of Assignor's interest assumed	100.00%
Total capital commitment	50,000
Partnership fees incurred	0	120
Capital contributions	$ 0	$ 1,341