Fair value measurements - Fair value hierarchy (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Net fair value presented on the unaudited consolidated balance sheets	$ 270,686	$ 51,929
Net fair value presented on the unaudited consolidated balance sheets	48,397	23,387
Liabilities:
Net fair value presented on the unaudited consolidated balance sheets	(875)	(7,698)
Net derivative asset (liability) positions	318,208	67,618
Commodity - Oil \| Commodity derivatives
Assets:
Net fair value presented on the unaudited consolidated balance sheets	222,125	6,422
Net fair value presented on the unaudited consolidated balance sheets	29,220	1,577
Liabilities:
Net fair value presented on the unaudited consolidated balance sheets	0	(348)
Commodity - Oil \| Deferred premiums
Assets:
Net fair value presented on the unaudited consolidated balance sheets	0	(477)
Liabilities:
Net fair value presented on the unaudited consolidated balance sheets	0	0
Commodity - Oil \| Contingent consideration
Liabilities:
Net fair value presented on the unaudited consolidated balance sheets	(875)	(7,350)
Commodity - NGL \| Commodity derivatives
Assets:
Net fair value presented on the unaudited consolidated balance sheets	32,721	12,490
Net fair value presented on the unaudited consolidated balance sheets	14,600	9,547
Liabilities:
Net fair value presented on the unaudited consolidated balance sheets	0	0
Commodity - Natural gas \| Commodity derivatives
Assets:
Net fair value presented on the unaudited consolidated balance sheets	15,840	33,494
Net fair value presented on the unaudited consolidated balance sheets	4,577	12,263
Liabilities:
Net fair value presented on the unaudited consolidated balance sheets	0	0
Net fair value presented on the unaudited consolidated balance sheets	0	0
Current Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	222,125	11,723
Amounts offset	0	(5,301)
Current Assets \| Commodity - Oil \| Deferred premiums
Assets:
Total gross fair value	0	0
Amounts offset	0	(477)
Current Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	32,721	13,787
Amounts offset	0	(1,297)
Current Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	17,582	33,494
Amounts offset	(1,742)	0
Noncurrent Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	29,220	1,577
Amounts offset	0	0
Noncurrent Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	14,600	9,547
Amounts offset	0	0
Noncurrent Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	4,382	12,263
Amounts offset	195	0
Current Liabilities \| Commodity - Oil \| Commodity derivatives
Liabilities:
Total gross fair value	0	(5,649)
Amounts offset	0	5,301
Current Liabilities \| Commodity - Oil \| Deferred premiums
Liabilities:
Total gross fair value	0	(477)
Amounts offset	0	477
Current Liabilities \| Commodity - Oil \| Contingent consideration
Liabilities:
Total gross fair value	(875)	(7,350)
Amounts offset	0	0
Current Liabilities \| Commodity - NGL \| Commodity derivatives
Liabilities:
Total gross fair value	0	(1,297)
Amounts offset	0	1,297
Current Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	(1,742)	0
Amounts offset	1,742	0
Noncurrent Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	195	0
Amounts offset	(195)	0
Level 1
Liabilities:
Net derivative asset (liability) positions	0	0
Level 1 \| Current Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 1 \| Current Assets \| Commodity - Oil \| Deferred premiums
Assets:
Total gross fair value	0	0
Level 1 \| Current Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 1 \| Current Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 1 \| Noncurrent Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 1 \| Noncurrent Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 1 \| Noncurrent Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 1 \| Current Liabilities \| Commodity - Oil \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 1 \| Current Liabilities \| Commodity - Oil \| Deferred premiums
Liabilities:
Total gross fair value	0	0
Level 1 \| Current Liabilities \| Commodity - Oil \| Contingent consideration
Liabilities:
Total gross fair value	0	0
Level 1 \| Current Liabilities \| Commodity - NGL \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 1 \| Current Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 1 \| Noncurrent Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 2
Liabilities:
Net derivative asset (liability) positions	318,208	68,095
Level 2 \| Current Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	222,125	11,723
Level 2 \| Current Assets \| Commodity - Oil \| Deferred premiums
Assets:
Total gross fair value	0	0
Level 2 \| Current Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	32,721	13,787
Level 2 \| Current Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	17,582	33,494
Level 2 \| Noncurrent Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	29,220	1,577
Level 2 \| Noncurrent Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	14,600	9,547
Level 2 \| Noncurrent Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	4,382	12,263
Level 2 \| Current Liabilities \| Commodity - Oil \| Commodity derivatives
Liabilities:
Total gross fair value	0	(5,649)
Level 2 \| Current Liabilities \| Commodity - Oil \| Deferred premiums
Liabilities:
Total gross fair value	0	0
Level 2 \| Current Liabilities \| Commodity - Oil \| Contingent consideration
Liabilities:
Total gross fair value	(875)	(7,350)
Level 2 \| Current Liabilities \| Commodity - NGL \| Commodity derivatives
Liabilities:
Total gross fair value	0	(1,297)
Level 2 \| Current Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	(1,742)	0
Level 2 \| Noncurrent Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	195	0
Level 3
Liabilities:
Net derivative asset (liability) positions	0	(477)
Level 3 \| Current Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 3 \| Current Assets \| Commodity - Oil \| Deferred premiums
Assets:
Total gross fair value	0	0
Level 3 \| Current Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 3 \| Current Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 3 \| Noncurrent Assets \| Commodity - Oil \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 3 \| Noncurrent Assets \| Commodity - NGL \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 3 \| Noncurrent Assets \| Commodity - Natural gas \| Commodity derivatives
Assets:
Total gross fair value	0	0
Level 3 \| Current Liabilities \| Commodity - Oil \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 3 \| Current Liabilities \| Commodity - Oil \| Deferred premiums
Liabilities:
Total gross fair value	0	(477)
Level 3 \| Current Liabilities \| Commodity - Oil \| Contingent consideration
Liabilities:
Total gross fair value	0	0
Level 3 \| Current Liabilities \| Commodity - NGL \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 3 \| Current Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	0	0
Level 3 \| Noncurrent Liabilities \| Commodity - Natural gas \| Commodity derivatives
Liabilities:
Total gross fair value	$ 0	$ 0

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