Commitments and Contingencies Schedule of expenses and losses incurred but not reported and accrued workers' compensation (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Pre-funded premiums for losses incurred but not reported	$ 732	$ 988
Accrued automobile and workers’ compensation claims	$ 867	$ 450