Fair value measurements - Fair value hierarchy (Details) - USD ($) $ in Thousands | Jun. 30, 2018 | Dec. 31, 2017 |
Assets: | | |
Derivative asset, current | $ 8,059 | $ 6,892 |
Derivative asset, noncurrent | 3,074 | 3,413 |
Liabilities: | | |
Derivative liability, current | (44,119) | (22,950) |
Derivative liability, noncurrent | (5,876) | (384) |
Recurring | | |
Liabilities: | | |
Net derivative position | (38,862) | (13,029) |
Recurring | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative asset, current | 5,402 | 3,706 |
Derivative asset, noncurrent | 457 | 5,526 |
Liabilities: | | |
Derivative liability, current | (37,039) | (8,756) |
Derivative liability, noncurrent | (2,686) | 3,698 |
Recurring | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative asset, current | (2,703) | (87) |
Derivative asset, noncurrent | 0 | (2,113) |
Liabilities: | | |
Derivative liability, current | (14,279) | (18,115) |
Derivative liability, noncurrent | (6,354) | (5,016) |
Recurring | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative asset, current | 0 | 0 |
Derivative asset, noncurrent | 0 | 0 |
Liabilities: | | |
Derivative liability, current | (3,697) | 0 |
Derivative liability, noncurrent | 0 | 0 |
Recurring | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative asset, current | 6,596 | 5,729 |
Derivative asset, noncurrent | 2,617 | 0 |
Liabilities: | | |
Derivative liability, current | 11,350 | 4,817 |
Derivative liability, noncurrent | 3,164 | 934 |
Recurring | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative asset, current | (1,236) | (2,456) |
Derivative asset, noncurrent | 0 | 0 |
Liabilities: | | |
Derivative liability, current | (454) | (896) |
Derivative liability, noncurrent | 0 | 0 |
Recurring | Current Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Amounts offset | (20,029) | (3,721) |
Recurring | Current Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Amounts offset | (2,703) | (87) |
Recurring | Current Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Amounts offset | 0 | 0 |
Recurring | Current Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Amounts offset | (11,163) | (4,817) |
Recurring | Current Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Amounts offset | (1,236) | (2,456) |
Recurring | Noncurrent Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Amounts offset | (6,217) | (6,087) |
Recurring | Noncurrent Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Amounts offset | 0 | (2,113) |
Recurring | Noncurrent Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Amounts offset | 0 | 0 |
Recurring | Noncurrent Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Amounts offset | (3,470) | (934) |
Recurring | Noncurrent Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Amounts offset | 0 | 0 |
Recurring | Other current liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Amounts offset | 20,029 | 3,721 |
Recurring | Other current liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Amounts offset | 2,703 | 87 |
Recurring | Other current liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Amounts offset | 0 | 0 |
Recurring | Other current liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Amounts offset | 11,163 | 4,817 |
Recurring | Other current liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Amounts offset | 1,236 | 2,456 |
Recurring | Noncurrent Liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Amounts offset | 6,217 | 6,087 |
Recurring | Noncurrent Liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Amounts offset | 0 | 2,113 |
Recurring | Noncurrent Liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Amounts offset | 0 | 0 |
Recurring | Noncurrent Liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Amounts offset | 3,470 | 934 |
Recurring | Noncurrent Liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Amounts offset | 0 | 0 |
Recurring | Fair value | | |
Liabilities: | | |
Net derivative position | (38,862) | (13,029) |
Recurring | Fair value | Current Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 25,431 | 7,427 |
Recurring | Fair value | Current Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Fair value | Current Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Fair value | Current Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 17,759 | 10,546 |
Recurring | Fair value | Current Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Fair value | Noncurrent Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 6,674 | 11,613 |
Recurring | Fair value | Noncurrent Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Fair value | Noncurrent Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Fair value | Noncurrent Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 6,087 | 934 |
Recurring | Fair value | Noncurrent Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Fair value | Other current liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (57,068) | (12,477) |
Recurring | Fair value | Other current liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | (16,982) | (18,202) |
Recurring | Fair value | Other current liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (3,697) | 0 |
Recurring | Fair value | Other current liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 187 | 0 |
Recurring | Fair value | Other current liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | (1,690) | (3,352) |
Recurring | Fair value | Noncurrent Liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (8,903) | (2,389) |
Recurring | Fair value | Noncurrent Liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | (6,354) | (7,129) |
Recurring | Fair value | Noncurrent Liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Fair value | Noncurrent Liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (306) | 0 |
Recurring | Fair value | Noncurrent Liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | | |
Liabilities: | | |
Net derivative position | 0 | 0 |
Recurring | Level 1 | Current Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Current Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Current Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Current Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Current Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 1 | Other current liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Other current liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Other current liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Other current liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Other current liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 1 | Noncurrent Liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 2 | | |
Liabilities: | | |
Net derivative position | (13,836) | 15,654 |
Recurring | Level 2 | Current Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 25,431 | 7,427 |
Recurring | Level 2 | Current Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 2 | Current Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 2 | Current Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 17,759 | 10,546 |
Recurring | Level 2 | Current Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 2 | Noncurrent Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 6,674 | 11,613 |
Recurring | Level 2 | Noncurrent Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 2 | Noncurrent Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 2 | Noncurrent Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 6,087 | 934 |
Recurring | Level 2 | Noncurrent Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 2 | Other current liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (57,068) | (12,477) |
Recurring | Level 2 | Other current liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 2 | Other current liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (3,697) | 0 |
Recurring | Level 2 | Other current liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 187 | 0 |
Recurring | Level 2 | Other current liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 2 | Noncurrent Liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (8,903) | (2,389) |
Recurring | Level 2 | Noncurrent Liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 2 | Noncurrent Liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 2 | Noncurrent Liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | (306) | 0 |
Recurring | Level 2 | Noncurrent Liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | | |
Liabilities: | | |
Net derivative position | (25,026) | (28,683) |
Recurring | Level 3 | Current Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Current Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Current Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Current Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Current Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Assets | Oil derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Assets | Oil derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Assets | NGL derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Assets | Natural gas derivatives | Commodity derivatives | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Assets | Natural gas derivatives | Deferred Premiums | | |
Assets: | | |
Derivative assets before netting | 0 | 0 |
Recurring | Level 3 | Other current liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | Other current liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | (16,982) | (18,202) |
Recurring | Level 3 | Other current liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | Other current liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | Other current liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | (1,690) | (3,352) |
Recurring | Level 3 | Noncurrent Liabilities | Oil derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Liabilities | Oil derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | (6,354) | (7,129) |
Recurring | Level 3 | Noncurrent Liabilities | NGL derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Liabilities | Natural gas derivatives | Commodity derivatives | | |
Liabilities: | | |
Derivative liabilities before netting | 0 | 0 |
Recurring | Level 3 | Noncurrent Liabilities | Natural gas derivatives | Deferred Premiums | | |
Liabilities: | | |
Derivative liabilities before netting | $ 0 | $ 0 |