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v3.3.1.900

Components of deferred tax assets and liabilities (Details 3) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Deferred tax assets: |  |
Postretirement | $ 97,666 | $ 99,853
Compensation-related | 33,844 | 35,669
Alternative minimum tax credit carryforward | 28,173 | 23,678
Customer advances | 12,623 | 12,245
Asset retirement obligations | 8,694 | 7,894
Legal and environmental contingencies | 6,377 | 7,890
Other | 58,202 | 52,862
Total deferred tax assets | 245,579 | 240,091
Deferred tax liabilities: |  |
Depreciation and basis differences on property, plant and equipment | 791,368 | 773,160
Postretirement | 71,835 | 70,642
Intangible asset amortization | 23,950 | 22,810
Other | 36,906 | 46,637
Total deferred tax liabilities | 924,059 | 913,249
Valuation allowance | 8,990 | 8,852
Deferred Tax Liabilities, Net | $ (687,470) | $ (682,010)

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