Loss and loss adjustment expense reserves - Schedule of loss and loss adjustment expense reserves (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Loss and Loss Adjustment Expense Reserves [Abstract]
Case loss and loss adjustment expense reserves	$ 33,028	$ 34,307
Incurred but not reported loss and loss adjustment expense reserves	131,596	100,024
Loss and loss adjustment expense reserves	$ 164,624	$ 134,331