Components of total lease cost (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Lessee Disclosure [Abstract]
Total lease cost	$ 442,949	[1]
Operating lease cost	35,570
Short-term lease cost	301,373	[2]
Variable lease cost	106,006	[3]
Operating cash flows from operating leases	12,074
Investing cash flows from operating leases	24,129
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 25,360

[1] ⁽³⁾  Lease costs are either expensed on the accompanying statements of operations or capitalized on the accompanying balance sheets depending on the nature and use of the underlying ROU asset.

[2] ⁽¹⁾  Costs associated with short-term lease agreements relate primarily to operational activities where underlying lease terms are less than one year. This amount is significant as it includes drilling and completion activities and field equipment rentals, most of which are contracted for 12 months or less. It is expected that this amount will fluctuate primarily with the number of drilling rigs and completion crews the Company is operating under short-term agreements.

[3] ⁽²⁾  Variable lease payments include additional payments made that were not included in the initial measurement of the ROU asset and corresponding liability for lease agreements with terms longer than 12 months. Variable lease payments relate to the actual volumes transported under certain midstream agreements, actual usage associated with drilling rigs, completion crews, and vehicles, and variable utility costs associated with the Company’s leased office space. Fluctuations in variable lease payments are driven by actual volumes delivered and the number of drilling rigs and completion crews operating under long-term agreements.