General Accounting and Disclosure Matters - Property and Equipment (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Abstract]
Unevaluated or suspended exploratory drilling costs	$ 0		$ 0
Revenue Recognition [Abstract]
Revenue gross-up	$ 46,306,000	$ 70,236,000	$ 148,779,000	$ 245,245,000
Minimum
Property, Plant and Equipment [Abstract]
Property and equipment, useful life			3 years
Maximum
Property, Plant and Equipment [Abstract]
Property and equipment, useful life			20 years