Properties and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment
Proved Natural Gas and Crude Oil Properties	$ 3,842,942	$ 3,499,718
Unproved Natural Gas and Crude Oil Properties	1,841,589	1,874,671
Total Natural Gas and Crude Oil Properties	5,684,531	5,374,389
Equipment and other	94,654	62,093
Land and Buildings	15,274	12,165
Construction in Progress	171,600	122,591
Properties and equipment, at cost	5,966,059	5,571,238
Accumulated DD&A	(1,800,487)	(1,562,972)
Property, Plant and Equipment, Net	$ 4,165,572	$ 4,008,266