Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Summary of unevaluated properties excluded from oil and natural gas properties being amortized

A summary of the unevaluated property costs excluded from oil and natural gas properties being amortized at December 31, 2017, and the year in which the costs were incurred follows:

	December 31, 2017
	Costs Incurred During:
In thousands	2017		2016		2015		2014 and Prior		Total
Property acquisition costs	$	8,527	$	—	$	—	$	583,418	$	591,945
Exploration and development	6,948		20,675		24,470		165,419		217,512
Capitalized interest	30,762		25,220		28,303		57,655		141,940
Total	$	46,237	$	45,895	$	52,773	$	806,492	$	951,397