Income Tax (details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Tax Expense [Abstract]
Income tax charge from increased effective Oregon tax rate	$ 600,000
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	25,721,000	25,239,000
Differences Required To Be Flowed Through By Regulatory Commissions	1,433,000	1,512,000
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	(169,000)	(791,000)
Income Tax Expense (Benefit)	$ 26,985,000	$ 25,960,000
Effective Income Tax Rate	41.60%	40.80%