Other comprehensive income (loss) and accumulated other comprehensive items (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ 1,999	$ (1,485)
Other comprehensive income before reclassifications	1,014	4,498
Amounts reclassified from other comprehensive items	0	0
Other comprehensive income	1,014	4,498
Ending Balance	3,013	3,013
Unrealized Gains/(Losses) On Marketable Securities, net of tax
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(234)	(203)
Other comprehensive income before reclassifications	31	0
Amounts reclassified from other comprehensive items	0	0
Other comprehensive income	31	0
Ending Balance	(203)	(203)
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	2,233	(1,282)
Other comprehensive income before reclassifications	983	4,498
Amounts reclassified from other comprehensive items	0	0
Other comprehensive income	983	4,498
Ending Balance	$ 3,216	$ 3,216