Property and equipment consisted of the following at June 30, 2021 and December 31, 2020 (in thousands):

	June 30, 2021			December 31, 2020
Equipment	$	7,578,343		$	7,647,451
Oil and natural gas properties		227,966			222,738
Buildings		184,921			193,503
Land		24,562			25,781
Total property and equipment		8,015,792			8,089,473
Less accumulated depreciation, depletion and impairment		(5,503,815	)		(5,328,432	)
Property and equipment, net	$	2,511,977		$	2,761,041

On a periodic basis, we evaluate our fleet of drilling rigs for marketability based on the condition of inactive rigs, expenditures that would be necessary to bring them to working condition and the expected demand for drilling services by rig type. The components comprising rigs that will no longer be marketed are evaluated, and those components with continuing utility to our other marketed rigs are transferred to other rigs or to our yards to be used as spare equipment. The remaining components of these rigs are retired. We had no impairment related to the marketability or condition of our drilling rigs during the three months and six months ended June 30, 2021.

We review our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amounts of certain assets may not be recovered over their estimated remaining useful lives (“triggering events”). In connection with this review, assets are grouped at the lowest level at which identifiable cash flows are largely independent of other asset groupings. We estimate future cash flows over the life of the respective assets or asset groupings in our assessment of impairment. These estimates of cash flows are based on historical cyclical trends in the industry as well as our expectations regarding the continuation of these trends in the future. Provisions for asset impairment are charged against income when estimated future cash flows, on an undiscounted basis, are less than the asset’s net book value. Any provision for impairment is measured at fair value.