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Income taxes - Significant Components of our deferred tax assets & liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Deferred tax assets: |  |
Accrued postretirement benefit cost | $ 69,725 | $ 78,518
Accrued liabilities | 4,679 | 1,080
Share-based compensation | 6,071 | 6,421
Goodwill | 5,539 | 7,949
Net operating losses and tax credits | 739,712 | 700,819
Foreign basis differences | 13,929 | 2,083
Ravenswood retiree legal settlement | 8,683 | 0
Other | 5,747 | 10,128
Total deferred tax assets | 854,085 | 806,998
Valuation allowance | (839,082) | (768,764)
Net deferred tax assets | 15,003 | 38,234
Deferred tax liabilities: |  |
Tax over financial statement depreciation | (119,378) | (125,386)
Unremitted foreign earnings | (808) | (18,901)
Total deferred tax liabilities | (120,186) | (144,287)
Net deferred tax liability | $ (105,183) | $ (106,053)

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