Property and equipment - Other property and equipment information (Details) $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) $ / Boe	Mar. 31, 2019 USD ($) $ / Boe
Property, Plant and Equipment [Abstract]
Capitalized employee-related costs	$ 4,505	$ 6,682
Depletion expense of evaluated oil and natural gas properties	$ 57,752	$ 59,370
Depletion expense (USD per BOE) \| $ / Boe	7.33	8.76

The noncash expense charged against earnings to recognize the consumption of oil and gas reserves that are part of an entities' assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Name:	us-gaap_DepletionOfOilAndGasProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration