Asset Retirement Obligations Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Start	$ 50,548		$ 42,914
Asset Retirement Obligation, Liabilities Incurred	146		5,411
Asset Retirement Obligation, Liabilities Settled	(2,617)		(1,081)
Asset Retirement Obligation, Accretion Expense	2,685		2,568
Asset Retirement Obligation, Revision of Prior Estimate	1,089	[1]	736	[1]
Asset Retirement Obligation, Period End	51,851		50,548
Electric Utilities [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Start	6,981		3,064
Asset Retirement Obligation, Liabilities Incurred	0		3,626
Asset Retirement Obligation, Liabilities Settled	0		0
Asset Retirement Obligation, Accretion Expense	168		291
Asset Retirement Obligation, Revision of Prior Estimate	(227)	[1]	0	[1]
Asset Retirement Obligation, Period End	6,922		6,981
Gas Utilities [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Start	259		270
Asset Retirement Obligation, Liabilities Incurred	0		0
Asset Retirement Obligation, Liabilities Settled	0		(22)
Asset Retirement Obligation, Accretion Expense	15		11
Asset Retirement Obligation, Revision of Prior Estimate	0	[1]	0	[1]
Asset Retirement Obligation, Period End	274		259
Coal Mining [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Start	20,286		17,158
Asset Retirement Obligation, Liabilities Incurred	3		1,627
Asset Retirement Obligation, Liabilities Settled	(714)		0
Asset Retirement Obligation, Accretion Expense	1,052		921
Asset Retirement Obligation, Revision of Prior Estimate	0	[1]	580	[1]
Asset Retirement Obligation, Period End	20,627		20,286
Oil and Gas [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Period Start	23,022		22,422
Asset Retirement Obligation, Liabilities Incurred	143		158
Asset Retirement Obligation, Liabilities Settled	(1,903)		(1,059)
Asset Retirement Obligation, Accretion Expense	1,450		1,345
Asset Retirement Obligation, Revision of Prior Estimate	1,316	[1]	156	[1]
Asset Retirement Obligation, Period End	$ 24,028		$ 23,022

[1] The Revisions to Prior Estimates reflects the change in the estimated liability for final reclamation adjusted for inflation, discount rate and market risk premium.