Cash Deposits and Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance collateral deposits	$ 1,453	$ 3,767
Excess loss fund	1,916	2,284
Accumulated interest income	788	814
State collateral deposits	57	57
Materials and supplies	443	273
Other	0	37
Total	4,657	$ 7,232
Letters of credit outstanding	$ 4,200