v2.4.0.6

Accounting for derivative instruments and hedging activities (Details 5) (Derivative instruments not designated as cash flow hedges, USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Unrealized gains and (losses) |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | $ (59,272) | $ (14,594) | $ 3,275
Natural gas swaps | Realized (gains) and losses |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | 43,470 |  |
Natural gas swaps | Unrealized gains and (losses) |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | (1,241) | (2,357) | (148)
Gas purchase agreements | Unrealized gains and (losses) |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | (56,954) |  |
Interest rate swaps | Realized (gains) and losses |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | 4,584 | 4,166 | 1,664
Interest rate swaps | Unrealized gains and (losses) |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | (1,077) | (12,237) | 3,423
Foreign currency forward contracts | Realized (gains) and losses |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | (18,483) | 5,201 | (6,625)
Foreign currency forward contracts | Unrealized gains and (losses) |  |  |
Impact of derivative instruments on the consolidated statements of operations |  |  |
Gains and losses for derivative instruments | $ 11,956 | $ 14,211 | $ (3,542)

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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 + Details
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