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Income taxes - Narrative (Details) - USD ($) $ in Thousands |  | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 21, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Mar. 31, 2017
Income taxes |  |  |  |  |  |  |  |  |
U.S. statutory rate | 21.00% |  | 21.00% | 35.00% |  | 35.00% |  |  |
Income tax Expense |  |  |  |  | $ 54,100 |  |  |  |
Change in income tax expense |  |  |  |  | 52,200 |  |  |  |
Net non-current deferred tax assets | $ 30,768 | $ 30,768 | $ 60,355 |  | 30,768 |  | $ 19,803 |  |
Net non-current deferred tax liabilities | 41,746 | 41,746 | 49,736 |  | 41,746 |  | 42,906 |  |
Non-cash charge |  |  |  |  | 73,400 |  |  |  |
Total foreign tax credit carryforwards | 175,229 | 175,229 |  |  | 175,229 |  | 153,169 |  |
Foreign tax credit expired |  |  |  |  |  |  |  |  | $ 19,500
Foreign tax credit carryforwards |  | 37,700 |  |  | $ 37,900 |  |  |  |
Tax credit carryforwards, years |  |  |  |  | 7 years |  |  |  |
Federal net operating loss carryforward utilization limit | 382,000 | 382,000 |  |  | $ 382,000 |  |  |  |
Foreign tax credit utilization limit | 383,000 | 383,000 |  |  | 383,000 |  |  |  |
Unrecognized tax benefits | 2,492 | 2,492 | 2,500 |  | 2,492 |  | 3,338 | $ 3,921 |
Operating loss carryforwards | 34,500 | 34,500 |  |  | 34,500 |  |  |  |
Unrecognized tax benefits that would have a favourable impact on effective tax rate | 2,200 | 2,200 | $ 2,200 |  | 2,200 |  |  |  |
Accrued interest and penalties | 800 | 800 |  |  | 800 |  | 800 | 700 |
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense |  |  |  |  | 0 |  | 100 | $ 200 |
Decrease in Unrecognized Tax Benefits is Reasonably Possible | 400 | 400 |  |  | 400 |  |  |  |
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations |  |  |  |  | 989 |  | 603 |  |
Effective Income Tax Rate Reconciliation, Tax Settlement, Foreign, Amount |  |  |  |  | 283,700 |  |  |  |
Brookfield Asset Management Inc |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Traded senior notes |  |  |  |  |  |  | $ 53,000 |  |
Foreign Tax Authority |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Deferred Tax Assets, Operating Loss Carryforwards | 3,700 | 3,700 |  |  | 3,700 |  |  |  |
Domestic Tax Authority |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Deferred Tax Assets, Operating Loss Carryforwards | 101,900 | 101,900 |  |  | 101,900 |  |  |  |
Operating loss carryforwards | 388,800 | 388,800 |  |  | 388,800 |  |  |  |
State and Local Jurisdiction |  |  |  |  |  |  |  |  |
Income taxes |  |  |  |  |  |  |  |  |
Operating loss carryforwards | $ 263,100 | $ 263,100 |  |  | $ 263,100 |  |  |  |

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