Supplemental Gas Data Exploratary Wells (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Development Wells Drilled, Net Productive	36	133	180
Costs expensed due to determination of dry hole or abandonment of project	$ 0	$ 0	$ 2,041
Costs reclassified to wells, equipment and facilities based on the determination of proved reserves	$ 40,917	$ 17,179	$ 27,453
Exploratory Wells Drilled, Net Productive		3	9