Income Tax (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Income Tax [Abstract]
Income tax expense (benefit)	$ (56,489,000)	$ 0	$ (56,454,000)	$ 0
Reversal of valuation allowance on deferred tax assets	57,600,000
Gross unrecognized tax benefits	1,600,000		1,600,000		1,900,000
Accumulated Other Comprehensive Income Loss [Line Items]
Income tax expense (benefit)	(56,489,000)	0	(56,454,000)	0
Mepco [Member]
Valuation Allowance [Line Items]
Valuation allowance against deferred tax assets attributable to Mepco	1,000,000		1,000,000
Disproportionate Tax Effects from Cash Flow Hedges [Member]
Income Tax [Abstract]
Income tax expense (benefit)	1,444,000
Accumulated Other Comprehensive Income Loss [Line Items]
Income tax expense (benefit)	$ 1,444,000