Property and equipment

The following table presents the Company's property and equipment as of the dates presented:



(in thousands)	March 31, 2018			December 31, 2017
Evaluated oil and natural gas properties	$	6,240,743		$	6,070,940
Less accumulated depletion and impairment	(4,699,395		)	(4,657,466		)
Evaluated oil and natural gas properties, net	1,541,348			1,413,474

Unevaluated oil and natural gas properties not being depleted	160,097			175,865

Midstream service assets	173,408			171,427
Less accumulated depreciation and impairment	(35,464		)	(33,102		)
Midstream service assets, net	137,944			138,325

Depreciable other fixed assets	48,585			48,957
Less accumulated depreciation and amortization	(23,982		)	(23,150		)
Depreciable other fixed assets, net	24,603			25,807

Land	18,257			14,914

Total property and equipment, net	$	1,882,249		$	1,768,385

For the three months ended March 31, 2018 and 2017, depletion expense for the Company's evaluated oil and natural gas properties was $7.34 per barrel of oil equivalent ("BOE") sold and $6.45 per BOE sold, respectively.

The Company uses the full cost method of accounting for its oil and natural gas properties. Under this method, all acquisition, exploration and development costs, including certain employee-related costs incurred for the purpose of exploring for or developing oil and natural gas properties, are capitalized and depleted on a composite unit-of-production method based on proved oil, NGL and natural gas reserves. Such amounts include the cost of drilling and equipping productive wells, dry hole costs, lease acquisition costs, delay rentals and other costs related to such activities. Costs, including employee-related costs, associated with production and general corporate activities, are expensed in the period incurred. Sales of oil and natural gas properties, whether or not being depleted currently, are accounted for as adjustments of capitalized costs, with no gain or loss recognized, unless such adjustments would significantly alter the relationship between capitalized costs and proved reserves of oil, NGL and natural gas.

The following table presents capitalized employee-related costs for the periods presented:



	Three months ended March 31,
(in thousands)	2018		2017
Capitalized employee-related costs	$	6,529	$	5,210

The Company excludes the costs directly associated with the acquisition and evaluation of unevaluated properties from the depletion calculation until it is determined whether or not proved reserves can be assigned to the properties. The Company capitalizes a portion of its interest costs to its unevaluated properties. Capitalized interest becomes a part of the cost of the unevaluated properties and is subject to depletion when proved reserves can be assigned to the associated properties. All items classified as unevaluated properties are assessed on a quarterly basis for possible impairment. The assessment includes consideration of the following factors, among others: intent to drill, remaining lease term, geological and geophysical evaluations, drilling results and activity, the assignment of evaluated reserves and the economic viability of development if proved reserves are assigned. During any period in which these factors indicate an impairment, the cumulative drilling costs incurred to date for such property and all or a portion of the associated leasehold costs are transferred to the full cost pool and are then subject to depletion.

The following table presents costs incurred in the acquisition, exploration and development of oil and natural gas properties for the periods presented:



	Three months ended March 31,
(in thousands)	2018		2017
Property acquisition costs:
Evaluated	$	—	$	—
Unevaluated	—		—
Exploration costs	6,137		15,543
Development costs	149,038		111,158
Total costs incurred	$	155,175	$	126,701