Environmental Matters (details) (USD $)	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012		Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	$ 50,386,000		$ 45,235,000				$ 56,414,000
Environmental Current Liabilities	18,874,000		24,466,000				18,665,000
Environmental Regulatory Table [Abstract]
Cash Paid for Environmental Sites	75,620,000		71,124,000				58,989,000
Regulatory Assets, Noncurrent	384,453,000		382,255,000		362,472,000	362,290,000	364,132,000		367,536,000	325,692,000	323,371,000	343,085,000
Environmental Remediation Obligations [Abstract]
Damages Sought On Environmental Claims	50,000,000
Portland Harbor draft FS range	$169 million to $1.8 billion
Portland Harbor Number Of Potentially Responsible Parties	more than 100
Gasco Siltronic Sediments draft EE/CA range	$38.4 million to $350 million
Gasco Siltronic Sediments Project Liability	34,000,000
Gasco Siltronic Sediments Other Liability	4,400,000.0
Gasco Groundwater Source Control range	$14.5 million and $25 million
Gasco Siltronic Sediments [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	38,050,000		36,087,000				43,655,000
Environmental Current Liabilities	389,000		2,207,000				2,459,000
Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	2,793,000		3,160,000				3,547,000
Environmental Current Liabilities	1,678,000		1,767,000				1,400,000
Gasco Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	8,365,000		5,028,000				7,689,000
Environmental Current Liabilities	15,411,000		18,722,000				13,197,000
Siltronic Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	414,000		379,000				588,000
Environmental Current Liabilities	556,000		637,000				478,000
Central Service Center [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	386,000		396,000				424,000
Environmental Current Liabilities	80,000		140,000				0
Front Street [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	199,000		0				395,000
Environmental Current Liabilities	760,000		993,000				1,131,000
Other Environmental [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	179,000		185,000				116,000
Environmental Current Liabilities	0		0				0
Environmental Restoration Costs [Member]
Environmental Regulatory Table [Abstract]
Regulatory Assets, Noncurrent	$ 125,671,000	[1]	$ 121,144,000	[1]			$ 108,007,000	[1]

[1] Certain utility pension costs are approved for regulatory deferral, including amounts recorded to the pension balancing account, to mitigate the effects of higher and lower pension expenses. Pension costs that are deferred include an interest component when recognized in net periodic benefit costs. See Note 7.