Cash Deposits and Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Insurance collateral deposits	$ 2,252	$ 2,599
Excess loss fund	1,495	1,450
Accumulated interest income	777	812
State collateral deposits	51	143
Materials and supplies	320	354
Other	37	171
Total	$ 4,932	$ 5,529