Other comprehensive (loss) income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Before-Tax Amount
Other comprehensive income (loss)	$ (1,732)	$ (971)	$ 25,668	$ (21,640)
Tax Expense (Benefit)
Other comprehensive income (loss)	(108)	(64)	5,635	(4,189)
Net-of-Tax Amount
Other comprehensive (loss) income, net of taxes:	(1,624)	(907)	20,033	(17,451)
Net unrealized (losses) gains on investments
Before-Tax Amount
Change in net unrealized gains and losses on investments	4,560	(2,417)	22,766	(15,625)
Less: reclassification adjustment for net losses (gains) included in net income	(116)	(174)	152	(781)
Other comprehensive income (loss)	4,444	(2,591)	22,918	(16,406)
Tax Expense (Benefit)
Change in net unrealized gains and losses on investments	957	(507)	4,781	(3,281)
Less: reclassification adjustment for net losses (gains) included in net income	(24)	(37)	32	(164)
Other comprehensive income (loss)	933	(544)	4,813	(3,445)
Net-of-Tax Amount
Change in net unrealized gains and losses on investments	3,603	(1,910)	17,985	(12,344)
Less: reclassification adjustment for net gains included in net income	(92)	(137)	120	(617)
Other comprehensive (loss) income, net of taxes:	3,511	(2,047)	18,105	(12,961)
Foreign currency translation adjustments
Before-Tax Amount
Other comprehensive income (loss)	(6,176)	1,620	2,750	(5,234)
Tax Expense (Benefit)
Other comprehensive income (loss)	(1,041)	480	822	(744)
Net-of-Tax Amount
Other comprehensive (loss) income, net of taxes:	$ (5,135)	$ 1,140	$ 1,928	$ (4,490)