Income taxes - Narrative (Detail) $ in Thousands	Mar. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 141,931
Amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate	85,293
Accrued interest related to the gross unrecognized tax benefits excluded from the unrecognized tax benefits	14,770
Significant decrease in unrecognized tax benefits that is reasonably possible	$ 100,000