Income taxes - Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Discounting of loss and loss adjustment expense reserves	$ 786	$ 534	$ 330
Unearned premiums	1,774	1,567	1,634
Temporary differences in recognition of expenses	1,208	1,247	138
Net operating loss carryforward	9,282	6,798	7,048
Total deferred tax assets	13,050	10,146	9,150
Deferred tax liabilities:
Deferred acquisition costs	1,379	1,490	7,798
Unrealized gains (losses) on investments	3,366	(405)	2,435
Total deferred tax liabilities	4,745	1,085	10,233
Net deferred tax asset (liability)	$ 8,305	$ 9,061
Net deferred tax asset (liability)			$ (1,083)