Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Before-Tax Amount
Other comprehensive income	$ 5,327	$ (1,732)	$ 14,606	$ 25,668
Tax Expense (Benefit)
Other comprehensive income (loss)	738	(108)	3,231	5,635
Net-of-Tax Amount
Other comprehensive income (loss), net of taxes:	4,589	(1,624)	11,375	20,033
Net unrealized (losses) gains on investments
Before-Tax Amount
Change in net unrealized gains and losses on investments	1,164	4,560	19,056	22,766
Reclassification adjustment for realized gains and losses on investments	(221)	(116)	(349)	152
Other comprehensive income	943	4,444	18,707	22,918
Tax Expense (Benefit)
Change in net unrealized gains and losses on investments	244	957	4,001	4,781
Reclassification adjustment for realized gains and losses on investments	(46)	(24)	(73)	32
Other comprehensive income (loss)	198	933	3,928	4,813
Net-of-Tax Amount
Change in net unrealized gains and losses on investments	920	3,603	15,055	17,985
Reclassification adjustment for realized gains and losses on investments	(175)	(92)	(276)	120
Other comprehensive income (loss), net of taxes:	745	3,511	14,779	18,105
Foreign currency translation adjustments
Before-Tax Amount
Other comprehensive income	4,384	(6,176)	(4,101)	2,750
Tax Expense (Benefit)
Other comprehensive income (loss)	540	(1,041)	(697)	822
Net-of-Tax Amount
Other comprehensive income (loss), net of taxes:	$ 3,844	$ (5,135)	$ (3,404)	$ 1,928