Other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Before-Tax Amount
Change in net unrealized gains on investments, before-tax amount	$ 8,906	$ 4,245
Less: reclassification adjustment for net gains included in net loss, before-tax amount	(98)	(1,002)
Net unrealized gains, before-tax amount	8,808	3,243
Foreign currency translation adjustments, before-tax amount	5,357	(8,942)
Other comprehensive income (loss), before taxes	14,165	(5,699)
Tax Expense (Benefit)
Change in net unrealized gains on investments, tax	3,117	1,486
Less: reclassification adjustment for net gains included in net loss, tax	(34)	(351)
Net unrealized gains, tax	3,083	1,135
Foreign currency translation adjustments, tax	2,062	(2,443)
Other comprehensive income (loss), tax	5,145	(1,308)
Net-of-Tax Amount
Change in net unrealized gains on investments, net-of-tax amount	5,789	2,759
Less: reclassification adjustment for net gains included in net loss, net-of-tax amount	(64)	(651)
Net unrealized gains, net-of-tax amount	5,725	2,108
Foreign currency translation adjustments, net-of-tax amount	3,295	(6,499)
Other comprehensive income (loss), net of taxes	$ 9,020	$ (4,391)