Leases - Assets and Liabilities (Details) $ in Thousands	Jun. 30, 2019 USD ($)
Leases [Abstract]
Operating leased asset	$ 200,734
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating leased asset
Finance leased asset	$ 18,927
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap_PropertyPlantAndEquipmentNet
Total leased assets	$ 219,661
Operating lease liabilities, current	$ 58,162
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Operating lease liabilities, current
Finance lease liabilities, current	$ 7,897
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Operating lease liabilities, noncurrent	$ 142,356
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Operating lease liabilities, noncurrent
Finance lease liabilities, noncurrent	$ 7,831
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	usx:LongtermDebtGrossAndFinanceLeasesNoncurren
Total lease liabilities	$ 216,246