Commitments and contingencies (Aquiline commitment) (Details) - USD ($) $ in Thousands			9 Months Ended
	Nov. 07, 2014	Oct. 02, 2014	Sep. 30, 2016	Dec. 31, 2015
Aquiline Capital Partners II GP Offshore Ltd
Related Party Transaction [Line Items]
Total capital commitment			$ 50,000
Remaining capital commitment			2,934	$ 3,413
Western World | Aquiline Capital Partners II GP Offshore Ltd
Related Party Transaction [Line Items]
Total capital commitment		$ 10,000
Remaining capital commitment			587	683
Aquiline Financial Services Fund III LP
Related Party Transaction [Line Items]
Total capital commitment	$ 100,000
Remaining capital commitment			$ 70,174	$ 86,110