Supplemental Gas Data Acreages (Details) number in Thousands, a in Thousands, $ in Thousands	Dec. 31, 2016 USD ($) a	Dec. 31, 2015 USD ($)
Gas and Oil Acreage [Line Items]
Unproved Oil and Gas Property, Successful Effort Method | $	$ 1,116,282	$ 1,421,083
Proved Oil and Gas Property, Successful Effort Method | $	$ 2,016,916	$ 1,922,602
Productive Gas Wells, Number of Wells, Gross	17,314
Gas and Oil Acreage, Undeveloped, Net	30,038
unproved acreage gross	4,804,804
Gas and Oil Acreage, Unproved, Net	3,745,533
Total Acreage - Gross	5,389,087
Total Acreage - Net	4,316,853
Productive Gas Wells, Number of Wells, Net	12,846
Productive Oil Wells, Number of Wells, Gross	189
Productive Oil Wells, Number of Wells, Net	30
Gas and Oil Area, Developed, Gross	549,816
Gas and Oil Area, Developed, Net	541,282
Gas and Oil Area, Undeveloped, Gross	34,467