Fair value measurements - Fair value of net derivative instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets (at fair value):
Derivative instruments - commodity derivatives	$ 11,117	$ 10,089
Commodity derivatives – noncurrent portion	1,189	0
Liabilities (at fair value):
Commodity derivatives – current portion	0	(431)
Fair Value
Assets (at fair value):
Equity investments	50,427	0
Liabilities (at fair value):
Warrant liability – noncurrent portion	0	(11,902)
Fair Value, Recurring
Assets (at fair value):
Equity investments	50,427
Commodity derivatives - current portion - Net of fair value presented in CBS	11,117	10,089
Commodity derivatives - noncurrent portion - Net of fair value presented in CBS	1,189
Liabilities (at fair value):
Commodity derivatives - current portion - Net fair value presented in CBS	0	(431)
US Derivative Liability, Non Current, Subject to Master Netting Arrangement, after Offset	0
Net derivative instruments	12,306	9,658
Fair Value, Recurring | Common Stock
Assets (at fair value):
Equity investments	25,554
Fair Value, Recurring | Preferred Stock
Assets (at fair value):
Equity investments	24,873
Fair Value, Recurring | Fair Value
Assets (at fair value):
Equity investments	50,427
Derivative instruments - commodity derivatives	14,202	20,197
Commodity derivatives - current portion offset in the Consolidated Balance Sheet	(3,085)	(10,108)
Commodity derivatives – noncurrent portion	2,534
Commodity derivatives - Non-current portion offset in the Consolidated Balance Sheet	(1,345)
Liabilities (at fair value):
Commodity derivatives – current portion	(3,085)	(10,539)
Commodity derivatives - current portion - Offset in Consolidated Balance Sheet	3,085	10,108
Commodity derivatives – noncurrent portion	(1,345)
Warrant liability - noncurrent portion- Offset in the Consolidated Balance Sheet	1,345
Warrant liability – noncurrent portion		(11,902)
Net derivative instruments	12,306	(2,244)
Fair Value, Recurring | Fair Value | Common Stock
Assets (at fair value):
Equity investments	25,554
Fair Value, Recurring | Fair Value | Preferred Stock
Assets (at fair value):
Equity investments	24,873
Fair Value, Recurring | Level 1 | Fair Value
Assets (at fair value):
Equity investments	25,554
Derivative instruments - commodity derivatives	0	0
Commodity derivatives – noncurrent portion	0
Liabilities (at fair value):
Commodity derivatives – current portion	0	0
Commodity derivatives – noncurrent portion	0
Warrant liability – noncurrent portion		(11,902)
Net derivative instruments	0	(11,902)
Fair Value, Recurring | Level 1 | Fair Value | Common Stock
Assets (at fair value):
Equity investments	25,554
Fair Value, Recurring | Level 1 | Fair Value | Preferred Stock
Assets (at fair value):
Equity investments	0
Fair Value, Recurring | Level 2 | Fair Value
Assets (at fair value):
Equity investments	24,873
Derivative instruments - commodity derivatives	14,202	20,197
Commodity derivatives – noncurrent portion	2,534
Liabilities (at fair value):
Commodity derivatives – current portion	(3,085)	(10,539)
Commodity derivatives – noncurrent portion	(1,345)
Warrant liability – noncurrent portion		0
Net derivative instruments	12,306	9,658
Fair Value, Recurring | Level 2 | Fair Value | Common Stock
Assets (at fair value):
Equity investments	0
Fair Value, Recurring | Level 3 | Fair Value
Assets (at fair value):
Equity investments	0
Derivative instruments - commodity derivatives	0	0
Commodity derivatives – noncurrent portion	0
Liabilities (at fair value):
Commodity derivatives – current portion	0	0
Commodity derivatives – noncurrent portion	0
Warrant liability – noncurrent portion		0
Net derivative instruments	0	$ 0
Fair Value, Recurring | Level 3 | Fair Value | Common Stock
Assets (at fair value):
Equity investments	0
Fair Value, Recurring | Level 3 | Fair Value | Preferred Stock
Assets (at fair value):
Equity investments	$ 0