Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Before-Tax Amount
Other comprehensive income (loss)	$ 28,076	$ (25,797)	$ 10,558
Tax Expense (Benefit)
Other comprehensive income (loss)	6,004	(5,465)	2,524
Net-of-Tax Amount
Other comprehensive income (loss)	22,072	(20,332)	8,034
Foreign currency translation adjustments
Before-Tax Amount
Other comprehensive income (loss)	8,337	(13,336)	11,050
Tax Expense (Benefit)
Other comprehensive income (loss)	1,859	(2,848)	2,696
Net-of-Tax Amount
Other comprehensive income (loss)	6,478	(10,488)	8,354
Net unrealized gains on investments
Before-Tax Amount
Change in net unrealized gains and losses on investments	19,220	(11,294)	2,718
Reclassification adjustment for change in unrealized gains and losses included in net income	519	(1,167)	(3,210)
Other comprehensive income (loss)	19,739	(12,461)	(492)
Tax Expense (Benefit)
Change in net unrealized gains and losses on investments	4,036	(2,372)	952
Reclassification adjustment for change in unrealized gains and losses included in net income	109	(245)	(1,124)
Other comprehensive income (loss)	4,145	(2,617)	(172)
Net-of-Tax Amount
Change in net unrealized gains and losses on investments	15,184	(8,922)	1,766
Reclassification adjustment for change in unrealized gains and losses included in net income	410	(922)	(2,086)
Other comprehensive income (loss)	$ 15,594	$ (9,844)	$ (320)