Contingent Liabilities and Commitments (Details) (USD $)	0 Months Ended			6 Months Ended		6 Months Ended
	Apr. 18, 2014	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Environmental assessment and remediation [Member]	Dec. 31, 2013 Environmental assessment and remediation [Member]	Jun. 30, 2014 Environmental assessment and remediation [Member] Minimum [Member]	Jun. 30, 2014 Environmental assessment and remediation [Member] Maximum [Member]	Jun. 30, 2014 Potentially responsible party at various Superfund and state waste disposal sites [Member]
Commitments and Contingencies Disclosure [Abstract]
Refund payments	$ 118,000,000
Site Contingency [Line Items]
Environmental assessment and remediation costs, low estimate				6,000,000
Environmental assessment and remediation costs, high estimate				8,000,000				500,000
Expected duration of environmental assessment and remediation spending						3 years	5 years
Accrued environmental assessment and remediation costs, total				3,300,000	4,100,000
Accrued environmental assessment and remediation costs, current				2,300,000	2,300,000
Accrued environmental assessment and remediation costs, noncurrent				1,000,000	1,800,000
Regulatory assets, total					1,800,000
Regulatory assets, current		48,601,000	37,520,000	1,200,000	1,200,000
Regulatory assets, noncurrent		$ 252,493,000	$ 256,612,000		$ 600,000