Summary of Significant Accounting Policies, Restricted Cash and Cash Equivalents (Details) (USD $)	1 Months Ended		12 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Restricted Cash [Abstract]
Restricted cash and cash equivalents			$ 14,221,000	$ 35,828,000
Diversified Lands Mitigation Escrow Agreement [Member]
Restricted Cash [Abstract]
Restricted cash and cash equivalents			97,000	97,000
Katrina/Rita Bond Payments [Member]
Restricted Cash [Abstract]
Restricted cash and cash equivalents			8,781,000	8,761,000
Collection net of operating expenses			20,100,000
Bond principal payments	6,400,000	6,700,000
Bond interest payments	3,400,000	3,600,000
Future Storm Restoration Costs [Member]
Restricted Cash [Abstract]
Restricted cash and cash equivalents			5,343,000	24,876,000
Increase (Decrease) in Restricted Cash and Cash Equivalents			(19,500,000)
Renewable Energy Grant [Member]
Restricted Cash [Abstract]
Restricted cash and cash equivalents			0	381,000
Nox Allowance Escrow [Member]
Restricted Cash [Abstract]
Restricted cash and cash equivalents			0	1,713,000
Transfer to Restricted Investments [Member] | Future Storm Restoration Costs [Member]
Restricted Cash [Abstract]
Restricted Cash and Cash Equivalents, Transfers			(10,900,000)
Transfer to cover storm related expenses [Member] | Future Storm Restoration Costs [Member]
Restricted Cash [Abstract]
Restricted Cash and Cash Equivalents, Transfers			(10,000,000)
Increase in Storm Surcredits [Member] | Future Storm Restoration Costs [Member]
Restricted Cash [Abstract]
Increase (Decrease) in Restricted Cash and Cash Equivalents			1,400,000
Decrease in NOx allowance escrow restricted cash account [Member] | Nox Allowance Escrow [Member]
Restricted Cash [Abstract]
Increase (Decrease) in Restricted Cash and Cash Equivalents			$ (1,700,000)