Leases and Right of Use Assets - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) tractor trailer
Lessee, Lease, Description [Line Items]
Number of tractors under lease | tractor	960
Number of trailers under lease | trailer	700
Operating lease, lease not yet commenced, payments due | $	$ 27.7
Lease rent expense | $	$ 0.0
Assets Held Under Finance Leases
Lessee, Lease, Description [Line Items]
Number of tractors under lease | tractor	606
Number of trailers under lease | trailer	651
Assets Held Under Operating Leases
Lessee, Lease, Description [Line Items]
Number of tractors under lease | tractor	354
Number of trailers under lease | trailer	49