Oil and natural gas activities (unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Abstract]

Costs incurred in oil and natural gas producing activities

Our oil and natural gas activities are conducted entirely in the United States. Costs incurred in oil and natural gas producing activities are as follows:

	Successor				Predecessor
	Period from		Period from		Period from		Period from
	January 1, 2018		March 22, 2017		January 1, 2017		January 1, 2016
	through		through		through		through
	December 31, 2018		December 31, 2017		March 21, 2017		December 31, 2016
Property acquisition costs
Proved properties	$	1,699	$	179	$	527	$	390
Unproved properties	120,610		33,901		2,904		15,497
Total acquisition costs	122,309		34,080		3,431		15,887
Development costs	199,833		140,180		32,657		114,472
Exploration costs	18,876		916		1,241		19,055
Total	$	341,018	$	175,176	$	37,329	$	149,414

Depreciation, depletion and amortization expense of oil and natural gas properties

Depreciation, depletion, and amortization expense of oil and natural gas properties was as follows: 

	Successor				Predecessor
	Period from		Period from		Period from		Period from
	January 1, 2018		March 22, 2017		January 1, 2017		January 1, 2016
	through		through		through		through
	December 31, 2018		December 31, 2017		March 21, 2017		December 31, 2016
DD&A (1)	$	79,070	$	84,899	$	23,442	$	115,765
DD&A per BOE:	$	10.56	$	12.86	$	13.05	$	12.97

________________________________

(1) Includes accretion of asset retirement obligations.

Oil and natural gas properties not subject to amortization

The costs of unevaluated oil and natural gas properties, by year incurred, consisted of the following:

	Year Cost Incurred
	2018		2017		2016		Total
Leasehold acreage (1)	$	91,175	$	324,501	$	11,530	$	427,206
Capitalized interest (2)	9,304		2,073		—		11,377
Wells in progress of completion	28,033		—		—		28,033
Total unevaluated oil and natural gas properties excluded from amortization	$	128,512	$	326,574	$	11,530	$	466,616

________________________________

(1) In the past, the costs associated with unevaluated properties typically related to historical acquisition costs of leasehold acreage. However, the year-end balance for 2018 includes an increase in carrying value to fair value of $299,397 as a result of the application of fresh start accounting upon emergence from bankruptcy. See “Note 4—Fresh start accounting.”

(2) As of December 31, 2018, this amount reflects the cumulative interest capitalized on the historical acquisition cost of leasehold acreage subsequent to our establishing opening balances under fresh start accounting. Interest is not capitalized on amounts related to the fair value gross up discussed above.