Other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Before-Tax Amount
Change in net unrealized gains on investments	$ 3,795	$ 8,906
Less: reclassification adjustment for net gains included in net income (loss)	(565)	(98)
Net unrealized gains	3,230	8,808
Foreign currency translation adjustments	1,680	5,357
Other comprehensive income	4,910	14,165
Tax Expense (Benefit)
Change in net unrealized gains on investments	1,328	3,117
Less: reclassification adjustment for net gains included in net income (loss)	(198)	(34)
Net unrealized gains	1,130	3,083
Foreign currency translation adjustments	355	2,062
Other comprehensive income	1,485	5,145
Net-of-Tax Amount
Change in net unrealized gains on investments	2,467	5,789
Less: reclassification adjustment for net gains included in net income (loss)	(367)	(64)
Net unrealized gains	2,100	5,725
Foreign currency translation adjustments	1,325	3,295
Other comprehensive income	$ 3,425	$ 9,020