Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Vessels [Member]
Fair Value Measurements [Abstract]
Fair market value of assets	$ 13,247	$ 12,550
Nonrecurring Basis [Member] | Prepaid Expenses and Other Current Assets [Member]
Fair Value Measurements [Abstract]
Fair market value of assets	220
Nonrecurring Basis [Member] | Vessels [Member]
Fair Value Measurements [Abstract]
Fair market value of assets	13,467
Nonrecurring Basis [Member] | Marine Transportation Equipment [Member]
Fair Value Measurements [Abstract]
Fair market value of assets	$ 13,247