Income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Income Tax [Line Items]
Provision for uncertain tax positions	$ 1,700		$ 1,700
Income tax expense	2,484	$ (7,781)	5,865	$ (5,768)
Deferred Tax Assets, Gross	5,600		5,600		$ 6,600
income tax expense - subsidiary [Member]
Income Tax [Line Items]
Income tax expense	1,372	(9,206)	1,053	(8,512)
Uncertain tax positions [Member]
Income Tax [Line Items]
Income tax expense	138	35	158	(615)
Withholding taxes [Member]
Income Tax [Line Items]
Income tax expense	$ 974	$ 1,390	$ 4,654	$ 3,359