Leases - Lease assets and liabilities (Details) - USD ($) $ in Thousands	Jul. 31, 2020	Jan. 31, 2020	Jul. 31, 2019
Assets and Liabilities, Lessee [Abstract]
Operating lease assets	$ 168,071	$ 270,032	$ 309,421
Classification of operating lease assets	us-gaap:OperatingLeaseRightOfUseAsset
Total lease assets	$ 168,071	270,032	309,421
Current operating lease liabilities	$ 91,700	63,166	74,297
Classification current operating lease liabilities	us-gaap:OperatingLeaseLiabilityCurrent
Noncurrent operating lease liabilities	$ 140,283	249,040	272,632
Classification of noncurrent operating liabilities	us-gaap:OperatingLeaseLiabilityNoncurrent
Total lease liabilities	$ 231,983	$ 312,206	$ 346,929