Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Income tax charge from increased effective Oregon tax rate			$ 600
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ (4,473)	$ (6,161)	15,848	$ 20,288
Differences Required To Be Flowed Through By Regulatory Commissions	(378)	(310)	1,036	1,184
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	298	(271)	(940)	(449)
Income Tax Expense (Benefit)	$ (4,553)	$ (6,742)	$ 15,944	$ 21,023
Effective Income Tax Rate	40.50%	43.60%	39.90%	41.00%