Properties, Plant and Equipment - Oil and Gas Properties - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) project	Mar. 31, 2016 USD ($) project
Oil and Gas Properties
Number of exploratory wells for which costs were capitalized | project	0	0
Costs capitalized in connection with exploratory wells	$ 0	$ 0
Exploration expense on exploratory wells	0	0
Amount of capitalized interest on expenditures	0	0
Depletion of oil and gas properties	35,400	41,500
Impairments of proved or unproved oil and gas properties	$ 0	$ 0