Income taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets [Abstract]
Unpaid losses and loss adjustment expenses	$ 8,199	$ 6,854
Unearned premiums	7,193	4,711
Organizational costs	162	196
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	765	557
State operating loss carryforwards	1,497	708
Allowance for doubtful accounts	570	551
Unrealized losses on fixed-maturity securities	0	837
Other	256	196
Deferred tax assets before allowance	18,642	14,610
Less: valuation allowance	(1,592)	(780)
Total deferred tax assets	17,050	13,830
Deferred tax liabilities [Abstract]
Unrealized gains on fixed-maturity securities	3,090	0
deferred tax liabilities, unrealized gains on equity securities	2,995	374
Deferred policy acquisition costs, net of ceding commissions	4,949	3,108
Intangible assets	743	743
Transition adjustment for loss discounting	1,537	2,060
Other	362	369
Total deferred tax liabilities	13,676	6,654
Net deferred tax assets	3,374	7,176
State Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 31,600	$ 19,500