Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) arising during the period, before income taxes	$ (6,664)	$ 9,563	$ (830)
Income taxes	1,399	(3,094)	290
Unrealized gains (losses) arising during the period, net of income tax	(5,265)	6,469	(540)
Less reclassification adjustment [Abstract]
Net realized investment gains (losses)	258	132	154
Income taxes	(54)	(47)	(54)
Reclassification adjustment included in net income	204	85	100
Other comprehensive income (loss)	(5,469)	6,384	(640)
Fixed Maturities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) arising during the period, before income taxes	(6,664)	5,371	(2,798)
Equity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gains (losses) arising during the period, before income taxes	$ 0	$ 4,192	$ 1,968