Segments - Long-lived assets by major geographic area (Details) - USD ($) $ in Thousands	Jan. 31, 2019	Apr. 30, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,352,590	$ 813,909
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	871,596	$ 813,909
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 480,994