Other comprehensive (loss) income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Before-Tax Amount
Change in net unrealized gains and losses on investments	$ (10,134)	$ 3,795
Less: reclassification adjustment for net gains included in net (loss) income	(315)	(565)
Net unrealized gains	(10,449)	3,230
Foreign currency translation adjustments	(2,279)	1,680
Other comprehensive (loss) income	(12,728)	4,910
Tax Expense (Benefit)
Change in net unrealized gains and losses on investments	(2,128)	1,328
Less: reclassification adjustment for net gains included in net (loss) income	(66)	(198)
Net unrealized gains	(2,194)	1,130
Foreign currency translation adjustments	(687)	355
Other comprehensive (loss) income	(2,881)	1,485
Net-of-Tax Amount
Change in net unrealized gains and losses on investments	(8,006)	2,467
Less: reclassification adjustment for net gains included in net (loss) income	(249)	(367)
Net unrealized gains	(8,255)	2,100
Foreign currency translation adjustments	(1,592)	1,325
Other comprehensive (loss) income	$ (9,847)	$ 3,425