Underwriting, acquisition and insurance expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Underwriting, Acquisition and Insurance Expenses [Abstract]
Direct commissions	$ 48,382	$ 36,885	$ 31,001
Ceding commissions	(12,347)	(10,448)	(9,799)
Other expenses	34,182	26,988	22,944
Total	70,217	53,425	44,146
Salaries, employee benefits and bonus expense	$ 27,800	$ 19,700	$ 17,700