Restructuring and Exit Costs - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring and exit-related costs	$ 0	$ 599,000
Eagle Ford Shale Area
Restructuring Cost and Reserve [Line Items]
Restructuring and exit-related costs			$ 1,100,000
Restructuring reserve	5,000
Mississippian Shale Area and Tuscaloosa Marine Shale Logistics Business
Restructuring Cost and Reserve [Line Items]
Restructuring and exit-related costs				$ 7,100,000
Mississippian Shale Area and Tuscaloosa Marine Shale Logistics Business | Accrued Liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 20,000