Other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Before-Tax Amount
Other comprehensive income	$ 26,306	$ 10,241	$ 9,279	$ 27,400
Tax Expense (Benefit)
Other comprehensive income	5,418	2,345	2,493	5,743
Net-of-Tax Amount
Other comprehensive income, net of taxes:	20,888	7,896	6,786	21,657
Net unrealized (losses) gains on investments
Before-Tax Amount
Change in net unrealized gains and losses on investments	21,159	6,800	17,892	18,206
Reclassification adjustment for realized gains and losses on investments	(27)	63	(128)	268
Other comprehensive income	21,132	6,863	17,764	18,474
Tax Expense (Benefit)
Change in net unrealized gains and losses on investments	4,444	1,429	3,757	3,824
Reclassification adjustment for realized gains and losses on investments	(6)	13	(27)	56
Other comprehensive income	4,438	1,442	3,730	3,880
Net-of-Tax Amount
Change in net unrealized gains and losses on investments	16,715	5,371	14,135	14,382
Reclassification adjustment for realized gains and losses on investments	(21)	50	(101)	212
Other comprehensive income, net of taxes:	16,694	5,421	14,034	14,594
Foreign currency translation adjustments
Before-Tax Amount
Other comprehensive income	5,174	3,378	(8,485)	8,926
Tax Expense (Benefit)
Other comprehensive income	980	903	(1,237)	1,863
Net-of-Tax Amount
Other comprehensive income, net of taxes:	$ 4,194	$ 2,475	$ (7,248)	$ 7,063