Income taxes Significant Components of our deferred tax assets & liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accrued postretirement benefit cost	$ 15,683	$ 12,851
Accrued liabilities	4,494	2,355
Share-based compensation	7,350	5,327
Derivative and hedging contracts	58,687	116,550
Goodwill	10,521	12,421
Equity contra - other comprehensive loss	81,567	61,216
Dual consolidated losses and capital losses	7,509	14,512
Net operating losses and tax credits	646,158	637,721
Foreign basis differences	668	0
Other	1,239us-gaap_DeferredTaxAssetsOther	1,533us-gaap_DeferredTaxAssetsOther
Total deferred tax assets	833,876us-gaap_DeferredTaxAssetsGross	864,486us-gaap_DeferredTaxAssetsGross
Valuation allowance	(748,283)	(765,023)
Net deferred tax assets	85,593us-gaap_DeferredTaxAssetsNet	99,463us-gaap_DeferredTaxAssetsNet
Tax over financial statement depreciation	(142,627)	(145,945)
Pension	(14,222)us-gaap_DeferredTaxLiabilitiesOther	(11,543)us-gaap_DeferredTaxLiabilitiesOther
Unremitted foreign earnings	(30,308)	(35,344)
Foreign basis differences	0	(790)
Total deferred tax liabilities	(187,157)us-gaap_DeferredIncomeTaxLiabilities	(193,622)us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax liability	$ (101,564)us-gaap_DeferredTaxLiabilities	$ (94,159)us-gaap_DeferredTaxLiabilities

The amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the tax basis and the basis in accordance with generally accepted accounting principles of foreign basis differences which will decrease future taxable income when such basis difference reverses.

No definition available.