Cash Deposits and Other Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance collateral deposits	$ 1,071	$ 1,453
Excess loss fund	821	1,916
Accumulated interest income	527	788
State collateral deposits	61	57
Materials and supplies	393	443
Total	$ 2,873	$ 4,657