Capitalized Exploratory Well Costs (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)
Capitalized Exploratory Well Costs [Abstract]
Capitalized exploratory well costs, beginning balance	$ 2.6
Additions to capitalized exploratory well costs pending the determination of proved reserves	11.0
Reclassification to proved properties after the determination of proved reserves	0.0
Capitalized exploratory well costs charged to expense	(0.1)
Capitalized exploratory well costs, ending balance	$ 13.5