Properties and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment
Proved Natural Gas and Crude Oil Properties	$ 3,183,772	$ 2,881,189
Unproved Natural Gas and Crude Oil Properties	61,838	60,498
Total Natural Gas and Crude Oil Properties	3,245,610	2,941,687
Equipment and other	31,410	30,098
Land and Buildings	10,900	12,667
Construction in Progress	107,794	113,115
Properties and equipment, at cost	3,395,714	3,097,567
Accumulated DD&A	(1,463,440)	(1,157,015)
Property, Plant and Equipment, Net	$ 1,932,274	$ 1,940,552