Leases - Lease assets and liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2021	Jan. 31, 2021	Apr. 30, 2020
Assets and Liabilities, Lessee [Abstract]
Operating lease assets	$ 180,715	$ 186,070	$ 251,565
Classification of operating lease assets	Operating lease assets
Total lease assets	$ 180,715	186,070	251,565
Current operating lease liabilities	$ 43,656	43,560	63,632
Classification current operating lease liabilities	Current operating lease liabilities
Noncurrent operating lease liabilities	$ 155,218	161,668	231,323
Classification of noncurrent operating liabilities	Noncurrent operating lease liabilities
Total lease liabilities	$ 198,874	$ 205,228	$ 294,955