The following table presents a summary of the Company’s property and equipment balances as of December 31, 2018 and 2017 (in thousands).



	December 31,
	2018			2017
Oil and natural gas properties
Evaluated (subject to amortization)	$	3,780,236		$	3,004,770
Unproved and unevaluated (not subject to amortization)	1,199,511			637,396
Total oil and natural gas properties	4,979,747			3,642,166
Accumulated depletion	(2,273,010		)	(2,021,169		)
Net oil and natural gas properties	2,706,737			1,620,997
Midstream and other property and equipment
Midstream equipment and facilities	424,480			258,725
Furniture, fixtures and other equipment	7,184			6,109
Software	8,039			7,942
Land	4,192			2,892
Leasehold improvements	6,171			5,428
Total midstream and other property and equipment	450,066			281,096
Accumulated depreciation	(33,939		)	(20,637		)
Net midstream and other property and equipment	416,127			260,459
Net property and equipment	$	3,122,864		$	1,881,456

The following table provides a breakdown of the Company’s unproved and unevaluated property costs not subject to amortization as of December 31, 2018 and the year in which these costs were incurred (in thousands).



Description	2018		2017		2016		2015 and prior		Total
Costs incurred for
Property acquisition	$	602,117	$	212,846	$	116,389	$	223,656	$	1,155,008
Exploration wells	12,361		1,235		712		204		14,512
Development wells	29,399		391		159		42		29,991
Total	$	643,877	$	214,472	$	117,260	$	223,902	$	1,199,511

Property acquisition costs primarily include leasehold costs paid to secure oil and natural gas mineral leases, but may also include broker and legal expenses, geological and geophysical expenses and capitalized internal costs associated with developing oil and natural gas prospects on these properties. Property acquisition costs are transferred into the amortization base on an ongoing basis as these properties are evaluated and proved reserves are established or impairment is determined. Unproved and unevaluated properties are assessed for possible impairment on a periodic basis based upon changes in operating or economic conditions.

Property acquisition costs incurred that remain in unproved and unevaluated property at December 31, 2018 are related almost entirely to the Company’s leasehold and mineral acquisitions in the Wolfcamp and Bone Spring plays in the Delaware Basin in Southeast New Mexico and West Texas during the past five years. These costs are associated with acreage for which proved reserves have yet to be assigned. A significant portion of these costs are associated with properties that are held by production or have automatic lease renewal options. As the Company drills wells and assigns proved reserves to these properties or determines that certain portions of this acreage, if any, cannot be assigned proved reserves, portions of these costs are transferred to the amortization base.

On September 12, 2018, the Company announced the successful acquisition of 8,400 gross and net leasehold acres in Lea and Eddy Counties, New Mexico for approximately $387 million in the Bureau of Land Management New Mexico Oil and Gas Lease Sale on September 5 and 6, 2018 (the “BLM Acquisition”). The BLM Acquisition was responsible for a significant portion of the Company’s property acquisition costs in 2018.

Costs excluded from amortization also include those costs associated with exploration and development wells in progress or awaiting completion at year-end. These costs are transferred into the amortization base on an ongoing basis as these wells are completed and proved reserves are established or confirmed. These costs totaled $44.5 million at December 31, 2018. Of this total, $14.5 million was associated with exploration wells and $30.0 million was associated with development wells. The Company anticipates that most of the $44.5 million associated with these wells in progress at December 31, 2018 will be transferred to the amortization base during 2019.