Fair value measurements - Fair value hierarchy (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Net fair value presented on the consolidated balance sheets	$ 7,893	$ 51,929
Net fair value presented on the consolidated balance sheets	0	23,387
Liabilities:
Net fair value presented on the consolidated balance sheets	(31,826)	(7,698)
Net fair value presented on the consolidated balance sheets	(12,051)	0
Net derivative asset (liability) positions	(35,984)	67,618
Interest Rate Contract
Liabilities:
Net fair value presented on the consolidated balance sheets	(206)	0
Net fair value presented on the consolidated balance sheets	(63)	0
Level 1
Liabilities:
Net derivative asset (liability) positions	0	0
Level 2
Liabilities:
Net derivative asset (liability) positions	(35,984)	68,095
Level 3
Liabilities:
Net derivative asset (liability) positions	0	(477)
Oil derivatives | Commodity derivatives
Assets:
Net fair value presented on the consolidated balance sheets	8,028	6,422
Net fair value presented on the consolidated balance sheets	0	1,577
Liabilities:
Net fair value presented on the consolidated balance sheets	(188)	(348)
Net fair value presented on the consolidated balance sheets	(10,932)	0
Oil derivatives | Deferred Premiums
Assets:
Net fair value presented on the consolidated balance sheets	0	(477)
Liabilities:
Net fair value presented on the consolidated balance sheets	0	0
Oil derivatives | Contingent Consideration
Liabilities:
Net fair value presented on the consolidated balance sheets	(665)	(7,350)
Net fair value presented on the consolidated balance sheets	(115)	0
Natural Gas Liquids | Commodity derivatives
Assets:
Net fair value presented on the consolidated balance sheets	0	12,490
Net fair value presented on the consolidated balance sheets	0	9,547
Liabilities:
Net fair value presented on the consolidated balance sheets	(13,465)	0
Net fair value presented on the consolidated balance sheets	0	0
Natural Gas | Commodity derivatives
Assets:
Net fair value presented on the consolidated balance sheets	(135)	33,494
Net fair value presented on the consolidated balance sheets	0	12,263
Liabilities:
Net fair value presented on the consolidated balance sheets	(17,302)	0
Net fair value presented on the consolidated balance sheets	(941)	0
Current Assets | Oil derivatives | Commodity derivatives
Assets:
Total gross fair value	32,958	11,723
Amounts offset	(24,930)	(5,301)
Current Assets | Oil derivatives | Deferred Premiums
Assets:
Total gross fair value	0	0
Amounts offset	0	(477)
Current Assets | Oil derivatives | Level 1 | Commodity derivatives
Assets:
Total gross fair value	0	0
Current Assets | Oil derivatives | Level 1 | Deferred Premiums
Assets:
Total gross fair value	0	0
Current Assets | Oil derivatives | Level 2 | Commodity derivatives
Assets:
Total gross fair value	32,958	11,723
Current Assets | Oil derivatives | Level 2 | Deferred Premiums
Assets:
Total gross fair value	0	0
Current Assets | Oil derivatives | Level 3 | Commodity derivatives
Assets:
Total gross fair value	0	0
Current Assets | Oil derivatives | Level 3 | Deferred Premiums
Assets:
Total gross fair value	0	0
Current Assets | Natural Gas Liquids | Commodity derivatives
Assets:
Total gross fair value	2,720	13,787
Amounts offset	(2,720)	(1,297)
Current Assets | Natural Gas Liquids | Level 1 | Commodity derivatives
Assets:
Total gross fair value	0	0
Current Assets | Natural Gas Liquids | Level 2 | Commodity derivatives
Assets:
Total gross fair value	2,720	13,787
Current Assets | Natural Gas Liquids | Level 3 | Commodity derivatives
Assets:
Total gross fair value	0	0
Current Assets | Natural Gas | Commodity derivatives
Assets:
Total gross fair value	521	33,494
Amounts offset	(656)	0
Current Assets | Natural Gas | Level 1 | Commodity derivatives
Assets:
Total gross fair value	0	0
Current Assets | Natural Gas | Level 2 | Commodity derivatives
Assets:
Total gross fair value	521	33,494
Current Assets | Natural Gas | Level 3 | Commodity derivatives
Assets:
Total gross fair value	0	0
Noncurrent Assets | Oil derivatives | Commodity derivatives
Assets:
Total gross fair value	0	1,577
Amounts offset	0	0
Noncurrent Assets | Oil derivatives | Level 1 | Commodity derivatives
Assets:
Total gross fair value	0	0
Noncurrent Assets | Oil derivatives | Level 2 | Commodity derivatives
Assets:
Total gross fair value	0	1,577
Noncurrent Assets | Oil derivatives | Level 3 | Commodity derivatives
Assets:
Total gross fair value	0	0
Noncurrent Assets | Natural Gas Liquids | Commodity derivatives
Assets:
Total gross fair value	0	9,547
Amounts offset	0	0
Noncurrent Assets | Natural Gas Liquids | Level 1 | Commodity derivatives
Assets:
Total gross fair value	0	0
Noncurrent Assets | Natural Gas Liquids | Level 2 | Commodity derivatives
Assets:
Total gross fair value	0	9,547
Noncurrent Assets | Natural Gas Liquids | Level 3 | Commodity derivatives
Assets:
Total gross fair value	0	0
Noncurrent Assets | Natural Gas | Commodity derivatives
Assets:
Total gross fair value	535	12,263
Amounts offset	(535)	0
Noncurrent Assets | Natural Gas | Level 1 | Commodity derivatives
Assets:
Total gross fair value	0	0
Noncurrent Assets | Natural Gas | Level 2 | Commodity derivatives
Assets:
Total gross fair value	535	12,263
Noncurrent Assets | Natural Gas | Level 3 | Commodity derivatives
Assets:
Total gross fair value	0	0
Current Liabilities | Interest Rate Contract
Liabilities:
Total gross fair value	(206)	0
Amounts offset	0	0
Current Liabilities | Level 1 | Interest Rate Contract
Liabilities:
Total gross fair value	0	0
Current Liabilities | Level 2 | Interest Rate Contract
Liabilities:
Total gross fair value	(206)	0
Current Liabilities | Level 3 | Interest Rate Contract
Liabilities:
Total gross fair value	0	0
Current Liabilities | Oil derivatives | Commodity derivatives
Liabilities:
Total gross fair value	(25,118)	(5,649)
Amounts offset	24,930	5,301
Current Liabilities | Oil derivatives | Deferred Premiums
Liabilities:
Total gross fair value	0	(477)
Amounts offset	0	477
Current Liabilities | Oil derivatives | Contingent Consideration
Liabilities:
Total gross fair value	(665)	(7,350)
Amounts offset	0	0
Current Liabilities | Oil derivatives | Level 1 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Current Liabilities | Oil derivatives | Level 1 | Deferred Premiums
Liabilities:
Total gross fair value	0	0
Current Liabilities | Oil derivatives | Level 1 | Contingent Consideration
Liabilities:
Total gross fair value	0	0
Current Liabilities | Oil derivatives | Level 2 | Commodity derivatives
Liabilities:
Total gross fair value	(25,118)	(5,649)
Current Liabilities | Oil derivatives | Level 2 | Deferred Premiums
Liabilities:
Total gross fair value	0	0
Current Liabilities | Oil derivatives | Level 2 | Contingent Consideration
Liabilities:
Total gross fair value	(665)	(7,350)
Current Liabilities | Oil derivatives | Level 3 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Current Liabilities | Oil derivatives | Level 3 | Deferred Premiums
Liabilities:
Total gross fair value	0	(477)
Current Liabilities | Oil derivatives | Level 3 | Contingent Consideration
Liabilities:
Total gross fair value	0	0
Current Liabilities | Natural Gas Liquids | Commodity derivatives
Liabilities:
Total gross fair value	(16,185)	(1,297)
Amounts offset	2,720	1,297
Current Liabilities | Natural Gas Liquids | Level 1 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Current Liabilities | Natural Gas Liquids | Level 2 | Commodity derivatives
Liabilities:
Total gross fair value	(16,185)	(1,297)
Current Liabilities | Natural Gas Liquids | Level 3 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Current Liabilities | Natural Gas | Commodity derivatives
Liabilities:
Total gross fair value	(17,958)	0
Amounts offset	656	0
Current Liabilities | Natural Gas | Level 1 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Current Liabilities | Natural Gas | Level 2 | Commodity derivatives
Liabilities:
Total gross fair value	(17,958)	0
Current Liabilities | Natural Gas | Level 3 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Interest Rate Contract
Liabilities:
Total gross fair value	(63)	0
Amounts offset	0	0
Noncurrent Liabilities | Level 1 | Interest Rate Contract
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Level 2 | Interest Rate Contract
Liabilities:
Total gross fair value	(63)	0
Noncurrent Liabilities | Level 3 | Interest Rate Contract
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Oil derivatives | Commodity derivatives
Liabilities:
Total gross fair value	(10,932)	0
Amounts offset	0	0
Noncurrent Liabilities | Oil derivatives | Contingent Consideration
Liabilities:
Total gross fair value	(115)	0
Amounts offset	0	0
Noncurrent Liabilities | Oil derivatives | Level 1 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Oil derivatives | Level 1 | Contingent Consideration
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Oil derivatives | Level 2 | Commodity derivatives
Liabilities:
Total gross fair value	(10,932)	0
Noncurrent Liabilities | Oil derivatives | Level 2 | Contingent Consideration
Liabilities:
Total gross fair value	(115)	0
Noncurrent Liabilities | Oil derivatives | Level 3 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Oil derivatives | Level 3 | Contingent Consideration
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Natural Gas Liquids | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Amounts offset	0	0
Noncurrent Liabilities | Natural Gas Liquids | Level 1 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Natural Gas Liquids | Level 2 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Natural Gas Liquids | Level 3 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Natural Gas | Commodity derivatives
Liabilities:
Total gross fair value	(1,476)	0
Amounts offset	535	0
Noncurrent Liabilities | Natural Gas | Level 1 | Commodity derivatives
Liabilities:
Total gross fair value	0	0
Noncurrent Liabilities | Natural Gas | Level 2 | Commodity derivatives
Liabilities:
Total gross fair value	(1,476)	0
Noncurrent Liabilities | Natural Gas | Level 3 | Commodity derivatives
Liabilities:
Total gross fair value	$ 0	$ 0