Components of total lease cost (Details) - USD ($) $ in Thousands			3 Months Ended	6 Months Ended
		Jan. 01, 2019	Jun. 30, 2019	Jun. 30, 2019
Lessee Disclosure [Abstract]
Total lease cost	[1]		$ 139,762	$ 315,066
Operating lease cost			11,479	20,458
Short-term lease cost	[2]		102,085	237,002
Variable lease cost	[3]		$ 26,198	57,606
Operating cash flows from operating leases				20,774
Right-of-use assets obtained in exchange for new operating lease liabilities		$ 50,000		$ 22,729

[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 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 and completion crews, 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.