Cash Deposits and Other Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance collateral deposits	$ 1,027	$ 1,453
Excess loss fund	794	1,916
Accumulated interest income	520	788
State collateral deposits	54	57
Materials and supplies	556	443
Total	$ 2,951	$ 4,657