Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Valuation of Financial Instruments by Pricing Levels

The following tables summarize the valuation of financial instruments by pricing levels that were accounted for at fair value on a recurring basis as of December 31, 2018 and 2017.

	Fair value measurements at December 31, 2018 using:
In thousands	Level 1		Level 2		Level 3		Total
Derivative assets:
Swaps	$	—	$	10,130	$	—	$	10,130
Collars	—		5,482		—		5,482
Total	$	—	$	15,612	$	—	$	15,612

	Fair value measurements at December 31, 2017 using:
In thousands	Level 1		Level 2		Level 3		Total
Derivative assets:
Swaps	$	—	$	2,603	$	—	$	2,603
Total	$	—	$	2,603	$	—	$	2,603

Unobservable inputs used in level 3 fair value measurements

Unobservable Input	Assumption
Future production	Future production estimates for each property
Forward commodity prices	Forward NYMEX strip prices through 2023 (adjusted for differentials), escalating 3% per year thereafter
Operating costs	Estimated costs for the current year, escalating 3% per year thereafter
Productive life of properties	Up to 50 years
Discount rate	10%

Unobservable inputs to the fair value assessment are reviewed quarterly and are revised as warranted based on a number of factors, including reservoir performance, new drilling, crude oil and natural gas prices, changes in costs, technological advances, new geological or geophysical data, or other economic factors. Fair value measurements of proved properties are reviewed and approved by certain members of the Company’s management.

Property Impairments

The following table sets forth the non-cash impairments of both proved and unproved properties for the indicated periods. Proved and unproved property impairments are recorded under the caption “Property impairments” in the consolidated statements of comprehensive income (loss).

	Year ended December 31,
In thousands	2018		2017		2016
Proved property impairments	$	18,037	$	82,340	$	2,895
Unproved property impairments	107,173		155,030		234,397
Total	$	125,210	$	237,370	$	237,292

Fair Values of Financial Instruments not Recorded at Fair Value

The following table sets forth the estimated fair values of financial instruments that are not recorded at fair value in the consolidated financial statements.

	December 31, 2018				December 31, 2017
In thousands	Carrying Amount		Estimated Fair Value		Carrying Amount		Estimated Fair Value
Debt:
Revolving credit facility	$	—	$	—	$	188,000	$	188,000
Note payable	7,700		7,700		9,974		9,900
5% Senior Notes due 2022	1,598,404		1,590,900		1,997,576		2,040,000
4.5% Senior Notes due 2023	1,488,960		1,476,300		1,486,690		1,526,800
3.8% Senior Notes due 2024	993,151		947,200		992,036		988,800
4.375% Senior Notes due 2028	988,617		942,800		988,061		987,200
4.9% Senior Notes due 2044	691,517		618,800		691,354		679,900
Total debt	$	5,768,349	$	5,583,700	$	6,353,691	$	6,420,600