Income taxes (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 151,098
Amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate	151,098
Accrued interest related to the gross unrecognized tax benefits excluded from the unrecognized tax benefits	22,618
Decrease in unrecognized tax benefits that is reasonably possible (up to)	$ 120,000