General Accounting and Disclosure Matters - Property and Equipment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Property, Plant and Equipment [Abstract]
Unevaluated or suspended exploratory drilling costs	$ 0		$ 0
Onshore normal leasehold period			3 years
Revenue Recognition [Abstract]
Revenue gross-up	$ 44,908,000	$ 99,082,000	$ 102,473,000	$ 175,009,000
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