Related party transactions (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Related Party Transaction [Line Items]
Gross premiums written	$ 87,587,000	$ 96,020,000
Narragansett Bay Insurance Company
Related Party Transaction [Line Items]
Gross premiums written	1,700,000	1,500,000
Pine Brook Road Partners, LLC
Related Party Transaction [Line Items]
Ownership percentage	12.00%		12.00%
Cayman Holdco
Related Party Transaction [Line Items]
Ownership percentage			10.00%
Ownership percentage	10.50%		10.00%
Estimated fair value of investment	43,000,000		29,300,000
Third Point Loan L.L.C | Investments in Securities and Derivative Contract
Related Party Transaction [Line Items]
Estimated fair value of investment	168,100,000		147,200,000
Third Point Hellenic Recovery US Feeder Fund, L.P.
Related Party Transaction [Line Items]
Ownership percentage	2.00%		2.00%
Committed capital	11,400,000
Committed capital, amount called	100,000
Committed capital, amount distributed	400,000	4,300,000
Estimated fair value of investment	$ 5,100,000		$ 5,300,000