Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Before-Tax Amount
Other comprehensive income (loss)	$ 24,678	$ 28,076	$ (25,797)
Tax Expense (Benefit)
Other comprehensive income (loss)	4,957	6,004	(5,465)
Net-of-Tax Amount
Other comprehensive income (loss)	19,721	22,072	(20,332)
Foreign currency translation adjustments
Before-Tax Amount
Other comprehensive income (loss)	5,777	8,337	(13,336)
Tax Expense (Benefit)
Other comprehensive income (loss)	988	1,859	(2,848)
Net-of-Tax Amount
Other comprehensive income (loss)	4,789	6,478	(10,488)
Net unrealized gains on investments
Before-Tax Amount
Change in net unrealized gains and losses on investments	19,548	19,220	(11,294)
Reclassification adjustment for realized gains and losses on investments	(647)	519	(1,167)
Other comprehensive income (loss)	18,901	19,739	(12,461)
Tax Expense (Benefit)
Change in net unrealized gains and losses on investments	4,105	4,036	(2,372)
Reclassification adjustment for realized gains and losses on investments	(136)	109	(245)
Other comprehensive income (loss)	3,969	4,145	(2,617)
Net-of-Tax Amount
Change in net unrealized gains and losses on investments	15,443	15,184	(8,922)
Reclassification adjustment for realized gains and losses on investments	(511)	410	(922)
Other comprehensive income (loss)	$ 14,932	$ 15,594	$ (9,844)