Revenues (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Abstract]
Revenues by major source	$ 541,159,000	$ 771,042,000	$ 1,185,085,000	$ 1,515,663,000
Revenue recognized			33,693,000	73,370,000
Contract assets	0		0		$ 0
Marine Transportation [Member]
Disaggregation of Revenue [Abstract]
Revenues by major source	380,987,000	404,286,000	784,244,000	772,407,000
Marine Transportation [Member] | Inland Transportation [Member]
Disaggregation of Revenue [Abstract]
Revenues by major source	303,012,000	310,162,000	621,577,000	593,247,000
Marine Transportation [Member] | Coastal Transportation [Member]
Disaggregation of Revenue [Abstract]
Revenues by major source	77,975,000	94,124,000	162,667,000	179,160,000
Distribution and Services [Member]
Disaggregation of Revenue [Abstract]
Revenues by major source	160,172,000	366,756,000	400,841,000	743,256,000
Distribution and Services [Member] | Oil and Gas [Member]
Disaggregation of Revenue [Abstract]
Revenues by major source	30,624,000	198,864,000	109,302,000	421,965,000
Distribution and Services [Member] | Commercial and Industrial [Member]
Disaggregation of Revenue [Abstract]
Revenues by major source	$ 129,548,000	$ 167,892,000	$ 291,539,000	$ 321,291,000