Income Taxes Deferred Tax Liability (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Assets, [Abstract]
Pension / postretirement benefits	$ 59,098	$ 41,898
NOL carryforward	0	51,941
Property taxes	18,025	0
Unbilled revenue	15,944	6,577
Customer advances	13,660	16,157
Reserves and accruals	12,457	4,378
Compensation accruals	11,303	7,269
AMT credit carryforwards	10,588	6,897
Environmental liability	9,701	9,670
Regulatory liability	1,526	1,098
QF obligations	1,462	20,596
Other, net	3,539	2,300
Valuation allowance	0	(3,834)
Deferred Tax Asset	157,303	164,947
Deferred Tax Liabilities, [Abstract]
Excess tax depreciation	(278,051)	(280,025)
Goodwill amortization	(118,313)	(96,233)
Flow through depreciation	(63,551)	(49,740)
Regulatory assets	(24,173)	(14,323)
Property taxes	0	(510)
Deferred Tax Liability	(484,088)	(440,831)
Deferred Tax Liability, net	$ (326,785)	$ (275,884)