Properties and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment
Proved Natural Gas and Crude Oil Properties	$ 3,759,501	$ 3,499,718
Unproved Natural Gas and Crude Oil Properties	1,559,717	1,874,671
Total Natural Gas and Crude Oil Properties	5,319,218	5,374,389
Equipment and other	104,568	62,093
Land and Buildings	10,714	6,392
Construction in Progress	177,341	122,591
Properties and equipment, at cost	5,611,841	5,565,465
Accumulated DD&A	(1,729,141)	(1,562,471)
Property, Plant and Equipment, Net	$ 3,882,700	$ 4,002,994