Risk Management and Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair value of derivative financial instruments
Current assets	$ 2,135	$ 3,901
Total derivatives assets	2,152	3,901
Current liabilities	4,371	6,469
Non-current liabilities and deferred credits	3,061	3,243
Total derivatives liabilities	7,432	9,712
Hedging instruments \| Commodity contracts \| Gas
Fair value of derivative financial instruments
Current assets	5
Non-current other assets	17
Current liabilities	219	476
Non-current liabilities and deferred credits	22
Hedging instruments \| Commodity contracts \| Electric
Fair value of derivative financial instruments
Current assets		1
Current liabilities	4,152	5,993
Non-current liabilities and deferred credits	3,039	3,243
Hedging instruments \| Transmission congestion rights (TCR) \| Electric
Fair value of derivative financial instruments
Current assets	$ 2,130	$ 3,900

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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