Leases and Right of Use Assets - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Apr. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) tractor trailer	Jun. 30, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Number of tractors under lease | tractor			1,012
Number of trailers under lease | trailer			810
Operating lease, lease not yet commenced, payments due		$ 26,100	$ 26,100
Lease rent expense		$ 40	80
Proceeds from obligation under finance lease	$ 10,500		$ 10,471	$ 0
Lessee, finance lease, term of contract	5 years
Sale leaseback transaction, monthly payment	$ 100
Sale leaseback transaction, historical cost, percent	32.50%
Assets Held Under Finance Leases
Lessee, Lease, Description [Line Items]
Number of tractors under lease | tractor			664
Number of trailers under lease | trailer			761
Assets Held Under Operating Leases
Lessee, Lease, Description [Line Items]
Number of tractors under lease | tractor			348
Number of trailers under lease | trailer			49